Transition
written by Iain Banks

The episode begins with Buck revealing he is a Vietnam War vet. Tara and Charmaine's parents pay a visit in order to celebrate the latter's birthday. However, they have a secret plan to get Kate and Marshall to live with them for a while, which Max rejects. He is determined to prevent Tara from slipping away this evening as her alters, especially Buck and T, will crash the party. The mood at the party is somewhat sullen, with Charmaine acting brattish. Kate leaves and goes to her boss's (Gene) apartment, where she begins a relationship with him. Tara's parents come out with the idea of taking the kids. Max, Tara, and Marshall are appalled. All the fuss pushes Charmaine to lose it, claiming that everyone has always paid more attention to Tara than her; then she flashes her lopsided boobs to everyone in the room. Although Tara seems to be fine right after the incident, Max wakes up in the middle of the night to find her urinating on her father

When a man is found badly beaten in a strip club parking lot, Detectives Benson and Stabler are at a loss for evidence as a rainstorm washed away any clues. A fake fingernail embedded in the victim's back leads the detectives to believe that the attacker is female. The victim, Mark Van Kuren (guest star Frank Grillo), awakes in the hospital with no memory of what happened, but brings the attention to his ex-wife Ellen (Wendy Makkena) and their 13-year-old transgender daughter Hailey (Bridger Zadina). It turns out that Hailey hated her father for not accepting her as a girl, which makes her the prime suspect, but the investigation soon leads to her guidance counselor (Aisha Hinds) instead. Daniela Sea guest stars as a transgender man.

Freamon and McNulty draw more attention to their fake serial killer by sensationalizing the murders. McNulty's compulsive behavior jeopardizes his relationship with Beadie Russell. Campbell learns of Daniels' history but convinces Burrell to leave quietly with the promise of a comfortable replacement position. Sergeant Ellis Carver puts his principles first in the Western District and his former partner Herc is shamed by his integrity. Stanfield convinces The Greeks to consider him an insurance policy and continues to assimilate Stewart's contacts including Maurice Levy. Omar returns to Baltimore and quickly learns that Stanfield was responsible for Butchie's death. Stewart prepares to leave town fearing reprisal from Omar but is once again betrayed by Cheese and murdered by Partlow as Stanfield watches.

Stephanie Healy, a bank worker, disappears after a rehearsal with her church choir. At first, she seems to be a normal working woman who has devoted herself to her religion, but the team discovers that she has severed all contact with her family and friends and that information about her past is extremely hard to come by. All is definitely not as it seems with Stephanie, and as the team finds out more about her mysterious history, they move closer to finding Stephaine. Vivian's heart condition is revealed to the rest of the team after she collapses while working.