It's been a tough night for Emma and Ethan, and things are about to get tougher when they find Sutton has disappeared after their argument and the Mercer family car is missing from the garage. When the police find the car at the bottom of the lake, Emma and Ethan look to each other for support, but Thayer threatens to tear them apart with his accusations against Ethan. Meanwhile, Char's aunt, Rebecca (guest star Charisma Carpenter, "Buffy the Vampire Slayer"), has returned to town and Char is the only one happy about it.

Ethan insists on helping Emma get the answers she's looking for about her twin sister. So when a tattoo sparks a memory about Sutton, Ethan pursues an explanation. But the information proves costly when Ethan heads into a situation that quickly gets out of control.

Meanwhile, Mads sneaks off to see Ryan, and Laurel continues to see Justin against her parents' wishes.

When Ethan is implicated in a serious crime, he and Sutton leave town and hide out with his father, Ben, on the reservation where he grew up. A burgeoning tension between father and son has Sutton playing mediator, but, despite the awkwardness, she appreciates seeing a side of Ethan that she did not know when they were together.

Meanwhile, Emma is left to deal with the aftermath of Ethan’s situation when she must pretend to be witness to a scene where she was not present.

An unexpected engagement leads to a quickly-planned wedding, causing suspicions that something is awry. Sutton encourages Emma to show Kristin what they found in Rebecca's house. And Ethan makes a discovery that changes the game.

Meanwhile, a shocking revelation leads to major repercussions in the Mercer household.

Emma and Thayer further their investigation into the twins' birth mother and what Sutton may know about her. Laurel begins to suspect that something is not right with her sister and makes everyone nervous when she starts asking questions. Using ammunition provided by Rebecca, Sutton lashes out at Kristin during what is supposed to be a peaceful Mercer family dinner.

Emma struggles to make sense of newfound revelations and shifts in her relationships with Ethan and Thayer. After hearing Emma's suspicions about Rebecca, Sutton's faith in her mother begins to falter and she decides to take matters into her own hands. Rebecca is thrilled when Kristin and Ted's marriage continues to unravel, putting her one step closer to achieving her goal. Meanwhile, Alec realizes that Jordan could be a strong ally in his private war with his wife.

Everyone gathers to celebrate Dan and Theresa's wedding but the celebrations do not go off as planned. Ethan figures out who Emma is protecting and confronts her about shutting him out. Sutton's sudden change of heart confuses Emma, who isn't sure she trusts her sister. Ted's behavior grows more erratic as his family continues to fall apart. Meanwhile, in the game between Alec and Rebecca, Jordan decides whose side he's on.

Ethan's confession to Dan threatens to shatter the brothers' relationship forever. Sutton receives a mysterious phone call that may provide some valuable information. Emma's feelings for Thayer are tested when she finds herself in close quarters with Ethan. And someone else comes face to face with Emma and Sutton.

Growing suspicions have everyone on edge. Dan gives Ethan an ultimatum with heartbreaking consequences and Emma finally confronts Rebecca.