City of Los Angeles in the year 2004, where secret agent Ana Lucia (Elizabeth Gutiérrez) has been given the mission of apprehending one of the most cunning and lethal criminal master minds in the country, Ricky Montana (Gabriel Porras). Ana Lucia (referred to as Analia by her fellow cops) goes undercover as a stripper in a club owned by Ricky Montana owned. Montana starts to fall for Analia and, lets her in on his mafia operations. However, after spotting Analia with a cop at the club, Ricky Montana grows doubts about his beloved stripper and starts to question her identity. Montana asks Analia to murder Mariana Montiel (Gaby Espino), a young and successful businesswoman who lives right there in Los Angeles. He knows that if Analia is indeed a cop, she will never agree to such a thing. Analia accepts the task.

Analia targets Mariana Montiel,who on her anniversary, unfortunately discovers that her husband, Daniel Montiel (Martin Karpan), has been cheating on her all along with her cousin, Sara Andrade (Maritza Rodríguez). She starts drinking heavily and leaves in Daniel's car the night of the anniversary party. Much to her surprise, she is stopped by an armed Analia, who forces herself into Mariana's car. Analia tells Mariana that she has been ordered to kill her, that she actually has no intention of hurting her, and that if she drives away at full speed, they will be able to lose Montana's men and hopefully fake the whole thing. But drunken Mariana has lost her will to live after discovering her husband's betrayal. She purposely drives the car off a cliff, where it falls hundreds of feet down into the road, explodes, and kills them both.

The explosion is witnessed by a mad scientist named Dr. Armando Rivera (Daniel Lugo), who was on his way home after a scholarly presentation on cell cloning. Dr. Rivera is able to retrieve Mariana's corpse from within the burning car, but Analia's body is nowhere to be found. Instead of calling an ambulance, Dr. Rivera takes Mariana to his laboratory where he intends to try out a new experiment that, if done properly, will bring Mariana back to life. The doctor is set on saving Mariana's life because his wife died in a similar fashion, and he was unable to do anything to save her. His operation is successful, but Mariana's body is still extremely burned, and thus, unrecognizable. His assistant, Roberto (Jorge Consejo), shows Dr. Rivera a purse he found close to the burning car. Assuming that it fell out of one of the car's windows during the fall and that it belongs to the woman the doctor had just resurrected, he shows him its contents. Inside the purse is a card that reads ‘ANALIA’ and a photograph of the cop. Dr. Rivera assumes this to be Mariana and sets out to reconstruct her face like that of Analia's. He and his assistant keep all this secret from the police in fear of going to jail for illegal experimentation on nonliving test subjects and unlicensed plastic surgical operations. Though it takes the doctor four years to make Mariana "as good as new," his work is so exceptionally well done that there is no physical trace of Mariana (now with the face of Analia) ever having experienced a car explosion. However, not everything turned out perfectly because, after much research on her part, an amnesiac Mariana—who believes herself to be Analia—realizes that if she is indeed who she thinks she is, going back to being an undercover cop and arresting Montana is the correct thing to do. Mariana is now forced to confront the dark and dangerous past of her "murderer." From this moment on, she will live a double life that unleashes a battle between love and, later on, her desire for vengeance.

Four years later,Mariana has fallen in love with none other than Daniel Montiel, but she does not realize he is in fact her husband—the same person who cheated on her with her cousin Sara. However, as their relationship develops, Daniel tells who he believes to be Analia of his life with his wife Mariana and the stupid mistake he made. It soon becomes evident that Mariana's cousin Sara had been the one who had pressured a weak Daniel into the affair. Furthermore, when Daniel and "Analia" start going out, Mariana's daughter Adrianita grows fond of who she does not realize is her mother. Unfortunately, Mariana's ambitious mother Carmen (Zully Montero) sees "Analia," unaware that she is indeed Mariana, as a threat to the family fortune, for if she marries Daniel, the Montiel inheritance might escape her greedy hands yet again.

Mariana, believing herself to be Analia, has now officially taken over the real Analia's mission, but nobody knows, not even herself, her true identity. "Retrained" (in reality, barely just trained for the first time) by the FBI, a new Mariana has her mind set on bringing down Montana and his operations. Mariana uses her sensuality to win Ricky Montana's heart, and the ignorant drug dealer once again falls for the woman who he believes to be the stripper Ana Lucia. But the story takes a twist when Mariana slowly starts to remember who she really is, that she is not Agent Analia, that she is not on a mission to bring down the drug trafficker Ricky Montana, and that her husband is actually the same man she is currently going out with. Coincidentally, at the same time, it is revealed that the real Analia is very much alive. Dr. Rivera had found her body a couple of days after the accident. He had taken her to his lab and resurrected her the same way he had resurrected Mariana. He had also reconstructed her face with the same advanced technology he had used during Mariana's surgery. (Obviously, this means that the doctor had found out about his mistake of putting Analia‘s face on Mariana, but he kept it a secret). The insane doctor Rivera had also fallen in love with Analia, and he kept her imprisoned in his lab all those years and conducted additional experiments on her. Now that Analia has escaped, she is determined on returning to her mission, which, unbeknownst to her, Mariana is currently working on.

Later, in an important subplot, we find out that Carmen isn’t Mariana's mother after all. Carmen, a former prostitute, married Mr. Andrade only for his money, and so Mr. Andrade looked for love in another woman. Olga (Elluz Peraza) (the other woman) becomes pregnant with Mariana at one point, but decides not to tell Mr. Andrade. Carmen finds out, and since she is sterile, she decides to steal baby Mariana at birth—a product of her husband and his affair. Now, years later, Olga has appeared and is looking for her adult daughter. Carmen tries to do everything in her power to prevent the truth from coming out, and after a few murders, she starts going insane and believes the spirits of the people she has killed are haunting her. These hallucinations drive Carmen to kill their maid and butler. She is sent to an asylum. She was spared from jail due to the fact that she was acting under a mental illness.

At around the same time, the two Analias meet and the truth about Dr. Rivera and the operations becomes clear to them both. They have no choice but to work together and bring down Montana. But when Montana hears about there being two Analias, things start to get complicated. He kidnaps one of the Analias (Mariana) and holds her hostage until the real Analia arrives. Much to his surprise, the real Analia admits that the police hired a look-alike to "trick him." Montana is still not buying it and has new suspicions about his beloved stripper. When he asks Analia where she has been these four years, she tells him that she was arrested for killing Mariana Montiel and has been in jail ever since, but finally managed to escape. When Analia realizes that Montana still doesn’t believe her tale and that the other Analia (Mariana) is in danger, Analia gets violent and demands to know why Montana won’t believe her. Her rage assures Montana that she is indeed the real Analia and he is forced to assume that she is telling the truth.

Montana plans to dispose of the fake Analia that night, so the real Analia asks Dr. Rivera for help. (Dr. Rivera had managed to clone Analia during the time he had held her prisoner. Agent Analia plans on switching Mariana—who is now unconscious due to Montana's drug injection—with a dead Analia clone, that way, since all three of them have the same face, Montana won’t be able to tell the difference and Mariana will hopefully be able to escape).

When Daniel finds out about his girlfriend's true identity and that she is actually his wife, he goes to save her, but Sara (who still has romantic interest in him) tags along, unaware of what Daniel is planning to do. Then, another secret comes out: Sara had been working with Montana all along. She was the one who had asked him to kill Mariana in the first place, so that when Mariana was out of the picture, she and Daniel could come out as a couple in public.

When Sara and Daniel arrive at Montana's, Montana assumes that Sara has betrayed him because she has shown up with the fake Analia's husband. He orders his men to burn Sara alive as punishment for her supposed treason, and Montana's henchmen are quick to follow directions. They lock the beautiful Sara in the trunk of a car and set it on fire. Unbeknownst to them however, Sara manages to escape before the car explodes, but she is badly burned and injured. Daniel also receives his punishment for trying to rescue his wife—he is beaten with a pipe by Montana's men and would have died from his injuries if it weren't for Analia and Mariana (who had just escaped from Montana's lair). Analia soon leaves after saving Daniel's life. She must return to Montana, who still believes her to be his lover. Dr. Rivera feels responsible for Daniel's attack, as it is his putting Analia's face on Mariana that started everything. The doctor comes to the conclusion that most hospitals would consider Daniel's condition mortal and would probably put him out of his pain with the practice of euthanasia. In order to mend his many errors, he decides to treat Daniel and his injuries himself. But unfortunately, now that the story about Mariana and the operation Rivera performed on her is out, it reaches injured Sara's ears, and the villainess sets to kidnap Dr. Rivera's assistant (Roberto) so that the doctor would be forced to operate on her too and give her back her beauty.

Dr. Rivera has no choice but to accept, treat Sara's injuries, and reconstruct her face. The operation, which was incredibly similar to that of Mariana's and Analia's, is a success—just like Daniel's. Both Mariana's husband and Mariana's evil cousin are safe.

While that is happening, Carmen seduces the psychiatrist that is treating her at the asylum. After the two have sex, Carmen convinces him to legally declare her as sane so that she could finally leave the asylum and be transferred to jail. The psychiatrist complies and the police go to the asylum to pick up Carmen, but she picks the lock to her handcuffs, strangles the cop in charge of transporting her, and escapes.

Times passes and Analia finally finds the perfect opportunity to arrest Montana. He will soon be meeting some Mexican smugglers at a dock outside of Los Angeles to receive the illegal merchandise. Analia plans on using the drugs Montana will be receiving as evidence for his trial. She will have to arrest him tonight. Montana, who now trusts Analia enough to let her come along, is unaware of what the undercover cop is planning on doing. When the smugglers arrive and meet up with Montana, Analia reveals herself to be a policewoman and tries to arrest the men, but Montana grows angry at her perceived betrayal and shoots randomly before making his escape. At the conclusion of the intense gun battle, Analia's backup arrest the Mexicans and Analia herself manages to trap Montana in an empty room of a nearby building. The two shoot at each other there and Montana manages to sneak up on Analia and knock her out momentarily. He attempts to rape her, but she wakes up and takes his gun. Analia forces Montana to his knees and humiliates him, but when Montana starts to talk trash about Analia's dead ex (who he killed prior to the beginning of the novela—the reason why Analia agreed to the mission in the first place), Analia loses her cool and tries to kill Montana, but is stopped by her fellow cops. Montana is arrested, and so are his men.

Montana's trial is quick to follow, and after Montana repeatedly mocks Analia and assures her he will escape, Analia insults him and assaults him, only to be heard by the judge and seen by the security guards. Analia is removed from the Montana case for unprofessional behavior, but she sees no point in being a cop if she cannot make Montana pay, so she quits her job as a policewoman.

In the trial, all of Montana's men declare against him—even his own lawyer. Montana is found guilty and given a life sentence in prison. Days later, the families of Montana's men are mysteriously attacked and the police conclude that Montana somehow is exacting his revenge from his cell. They find a cell phone in his cell and start an investigation as to how he obtained it. The police assume that Analia is next, seeing how Montana was in love with her and she betrayed him. Their suspicions are proven to be true when Analia's mother and sister are kidnapped, but the two women are soon rescued and the men responsible imprisoned. While everyone worries about how powerful Montana might be, even from behind bars, nobody pays attention to Carmen's escape from the asylum. Carmen, now disguised as a poor old beggar, plots the kidnapping of her political niece, Mariana and Daniel's daughter Adrianita. She spreads rumors of her crossing the border to Mexico and they reach the ears of the police, and when the police lessen security in L.A., stop the search for her in the United States and begin looking for her in Mexico, Carmen gathers old friends to help her kidnap her niece.

Soon after Montana's trial, the police find out that one among them is actually working for Montana and had given him the cell phone, along with the addresses of his men's homes so that the attacks, kidnappings, and bombings can be scheduled. When they discover who the traitor is, they also discover that Montana is planning his escape from jail. Captain Lares looks for Analia and begs her to return because he knows she is the only one who can stop Montana. Analia agrees and the captain gives her license to kill.

When Montana cleverly escapes from jail in a garbage truck, Analia (along with Mariana, Daniel, and Mariana's brother) chase after him. The epic battle continues in a park and both Analia and Montana each sustain multiple injuries. When Analia shoots Montana in the face, Montana falls to the ground, but not before pulling the trigger one last time, shooting Analia in the heart and killing her.

Montana is taken to a hospital and Analia is taken to Dr. Rivera, who manages to resurrect her for a second time. However, even though Dr. Rivera has managed to help Analia multiple times, the science he practices is unlicensed and thus illegal. The police are forced to arrest him, but try to convince the judge of his innocence.

Now that Montana is out of the picture, Sara decides it is time to get her revenge on Mariana. She intended to take over Mariana's company, but realizes that she is aging at an extremely accelerated pace. Dr. Rivera tricked her during the operation and coated her new synthetic skin with a substance that caused her to age rapidly when exposed to sunlight. Sara, caring so much about her beauty, kidnaps Mariana and Daniel, in hopes of persuading Dr. Rivera to re-operate. While pointing the gun at Mariana, she forces Daniel to drive out of the city, but Daniel tells Sara to kill both of them right there in the car or to prepare to die herself, because he's willing to crash the car. Daniel speeds up the driving and Sara grows worried. Mariana takes advantage of this and takes the gun from her. She and Daniel get out of the car before Sara can stop them. Mariana's brother had called the police and some cops had managed to catch up with them. When Sara sees police vehicles coming to her, preferring death to prison, she drives the car off the road and falls off a cliff, exploding in the same way that Daniel's first car exploded the night Analia and Mariana met. Meanwhile, Carmen is planning to kidnap Adrianita with the help of another woman. She attacks a police officer and takes his gun. She almost kills Adriana but is caught and sent to an asylum. Tries to escape but is killed there by some of the patients. At the end of the story, Analia decides to get Mariana's original face and Mariana discovers that she is pregnant.