Bridget goes on the run after witnessing a murder, hiding out by assuming the life of her wealthy identical twin sister Siobhan - only to learn that her sister's seemingly idyllic life is just as complicated and dangerous as the one she's trying to leave behind.
Bridget Kelly is six-months sober and starting to turn her life around when she is the sole witness in a murder trial. Despite the assurances of her FBI protector, Agent Victor Machado, Bridget knows her life is on the line. She flees to New York, telling no one, and reunites with her estranged twin, Siobhan Martin. Wealthy, pampered and married to the strikingly handsome Andrew Martin, Siobhan lives what appears to be a fairy tale life - a life where no one knows that Bridget exists. The sisters seem to be mending their frayed relationship - until Siobhan disappears mysteriously, and Bridget makes the split decision to take on her sister's identity. She discovers shocking secrets, not only about her sister and her marriage, but also about Siobhan's best friend, Gemma Butler and Gemma's husband, Henry.
Machado chooses to stay in New York City to thorough his research about Siobhan. Bridget, while trying to hide the body of her attacker, confides in her Narcotics Anonymous sponsor Malcolm Ward; together they develop a getaway plan for her. Siobhan's best friend Gemma and her husband Henry's fighting escalates and Bridget unexpectedly bonds with her rebellious stepdaughter Juliet. Siobhan is hiding out in Paris with an unknown agenda.
Bridget, Andrew, Gemma, and Henry head to the Hamptons to celebrate Siobhan's birthday, where Bridget reflects the rough past she and her sister experienced. In Paris, Siobhan uses her feminine charm to continue to lure Tyler closer to benefit her hidden motives for Bridget and Andrew. While Agent Machado uncovers crucial pieces of information, Bridget's situation worsens when secrets of her own are revealed, leaving the consequences of her lies unknown and in the hands of Gemma.
Gemma asks Bridget, who is still posing as Siobhan, to do her a favor that could cost Bridget everything. Henry is given some crushing news about his writing career, and Andrew has to deal with his tumultuous relationship with his teenage daughter Juliet. Bridget meets a potential new sponsor named Charlie at a local Narcotics Anonymous meeting, while Malcolm must face his demons when he is put in a position that could jeopardize his sobriety.
When Bridget cannot get in touch with Gemma she begins to wonder if something has happened between Gemma and Henry. Juliet starts a new school, where she defends herself against the school bully and her teacher Mr. Carpenter comes to her rescue. Bridget asks Charlie to do her a favor that could come back to haunt her, while Agent Machado looks into Malcolm's disappearance.
Still posing as Siobhan, Bridget is forced to reveal she has a twin to Andrew and Henry when Agent Machado starts closing in. Henry becomes a suspect in the whereabouts of his wife, Gemma and Juliet starts partying to dangerous extremes. Meanwhile, Malcolm escapes and is on the run from his kidnappers.
Andrew and Bridget are told some upsetting news that also affects Henry. Juliet continues to form an unlikely bond with her teacher Mr. Carpenter and Malcolm shows up in New York, where Agent Machado confronts him. Meanwhile, Siobhan's relationship with Tyler is jeopardized.
Bridget begins to realize she is developing feelings for Andrew, while Henry and Andrew’s business partner Olivia bond over common interests. Malcolm is suspicious of Bridget’s new NA sponsor Charlie and Bridget makes an appointment with Siobhan’s therapist, hoping it will help her discover some insight into her sister’s life.
Henry begins to target someone as a suspect in the disappearance of his wife Gemma and realizes he must work with Bridget to find out more information. Malcolm talks to the police about his suspicion of Charlie, while Juliet develops an unhealthy obsession with her teacher Mr. Carpenter. Meanwhile, Agent Machado meets with an informant back in Wyoming.
Bridget offers to host a fundraiser that her friend Greer is holding for Juliet's school and discovers that Greer knew one of Siobhan's deep dark secrets. While back in New York, Siobhan discovers that Bridget has settled into her former life more easily than Siobhan expected and she is determined to change that. Meanwhile, Malcolm decides to work for Andrew at Martin/Charles in order to keep an eye on him, and Henry mourns the death of his wife.
Juliet’s mother Catherine arrives in town, where she proceeds to wreak havoc on Andrew and Bridget’s relationship. Bridget discovers someone from Siobhan’s past and thinks he might be the key to her learning more information about her sister. Meanwhile, Henry discovers a lead that causes Agent Machado to think he is closing in on Bridget.
Bridget visits some of the last locations Siobhan went before she disappeared and discovers that Siobhan kept a secret office. Olivia finds out some information about Henry and blackmails him into introducing her to Gemma’s wealthy father Tim Arbogast. Meanwhile, in Paris, Tyler struggles with a moral decision that could affect Siobhan and Andrew.
Following her investigations from the last episode, Bridget takes Malcolm to Siobhan's secret office only to find it empty. Back in the Martin's apartment, Bridget gets a call that causes her to remember what drove her apart from her sister. Flashbacks from seven years ago reveal Siobhan's troubled relationship with Dylan, an ex-boyfriend who dumped her after she got pregnant, but after a few years wants to prove that he was a changed man. Bridget, who is babysitting Siobhan's son, Sean, allows Dylan to take Sean out just for one day despite Siobhan forbidding it. On their way home, Dylan asks Bridget if she can support him when he files to be Sean's legal guardian, and a car hits them in the middle of the road, killing Sean in the process. Back in the present day, Bridget, as Siobhan, forgives Dylan after understanding that what happened was an accident, and not necessarily their fault. In the meantime, after finding out that Henry has got the key to Siobhan's Safe deposit box, Malcolm, who's helping Bridget to find out who's chasing her, decides to keep an eye on Henry. Juliet's scheme takes a dark path when Tessa is brutally attacked after buying a car with Andrew's money, which causes Juliet to believe Mr. Carpenter did it. She then tells her father that she is willing to live with her mother in Miami for a "change of scenery." That leads to the revelation that Catherine was the one who had the idea for the scheme.
Andrew asks Bridget (thinking she is Siobhan) to renew their vows and they begin planning a wedding ceremony, with Juliet as the Maid of honor. Siobhan, visiting an OB/GYN in Paris, learns she is having twins but doesn't tell Henry that the conception date means the baby may be Andrew's. Malcolm is fired when he is caught stealing information from Olivia's computer, and later tells Bridget that Andrew's company is running a Ponzi scheme. Catherine is romantically involved with Mr. Carpenter but then steals his money and blackmails him into leaving Juliet alone. It is also revealed that Andrew came up with the Ponzi scheme and that Catherine paid someone to attack Tessa, but to roughen her up, not beat her severely.
Andrew confides in Bridget (who he thinks is Siobhan) about running a giant Ponzi scheme, which fills her with doubt and fear as she debates on what to do. Meanwhile, it is revealed that Agent Machado's past relationship with his informant, the murder victim/stripper Shaylene Briggs, was more than professional. Siobhan deceives Malcolm when she pretends to be Bridget in order to remove him from the scene. In Paris, Tyler takes something from Siobhan that is a key piece of evidence in her plot for revenge against Andrew. Andrew tells Olivia that Bridget (who is acting as Siobhan) is aware of their Ponzi scheme and she suggests they take action to keep Malcolm, Bridget (acting as Siobhan) and Tyler quiet. Also, Henry realizes Bridget knows more than she should and has to follow Siobhan's orders to keep Bridget from interfering with their plans.
Bridget fears that something has happened to Malcolm when she cannot get in touch with him.. In an effort to find him, Bridget visits the hotel where Malcolm was staying and discover on security footage that Andrew was the last person to see Malcolm before he disappeared. Meanwhile, Juliet discovers that someone in her family played a part in the attack on Tessa and Siobhan admits to Henry the reason she faked her death.
After an attempt made on Bridget's life results in Andrew being shot, Agent Machado is more determined than ever to find out who was responsible and what Bridget (still impersonating Siobhan) knows about it. Henry accuses Siobhan of putting a hit out on Bridget, which Siobhan denies, while Bridget thinks the missing Olivia was behind it as well as the murder of Tyler. Meanwhile, Andrew admits to asking Malcolm to leave town and Juliet tells Bridget the truth about her mother.
Henry grows impatient with Siobhan’s plan and tells her she needs to let go of her murderous revenge plot against both Andrew and Bridget or they cannot be together. Bridget decides that the only way she will feel safe is if she gives up her charade of impersonating Siobhan and returns to Wyoming to testify against the sadistic Bodaway Macawi. Agent Machado gets suspended from the FBI after he beats up a suspect in full view of witnesses. Later, he gets an idea to make Bodaway Macawi think Bridget's dead, since that's what he wants. The plan ends up going down terribly wrong and reveals that Catherine wants Siobhan dead.
Still posing as Siobhan, Bridget admits to Agent Machado that someone tried to kill her months earlier and she thought it was Andrew. Bridget goes to Henry’s apartment, where Siobhan overhears Bridget accuse Henry of Tyler’s murder. Meanwhile, Catherine goes to desperate extremes to bring Andrew closer to her.
Andrew catches Catherine trying to fake Bridget's suicide, so she holds them both hostage along with Juliet. Running out of options, Catherine calls Olivia, who is revealed to be her lover. Olivia tells Catherine to bring Bridget to her house, so they can run away together. When Catherine and Bridget arrive, Agent Machado arrests Catherine, having heard the conversation at the apartment after Bridget secretly calls him. Meanwhile, the main witness against Henry dies of a drug overdose and Siobhan gives birth to twin girls. Henry asks the nurse for a paternity test, showing his doubts about Siobhan.
As the vow renewal nears, Bridget realizes she first needs to tell Andrew the truth about who she really is. Meanwhile, just as Bodaway Macawi starts to close in on Bridget, Agent Machado is forced off the case and Henry decides whether he should tell Bridget the truth about Siobhan.