"Undertow" is the fifth episode of the second season of the HBO original series, The Wire. The episode was written by Ed Burns from a story by David Simon & Ed Burns and was directed by Steve Shill. It originally aired on June 29, 2003.

The title refers to the tide effect that traps unsuspecting swimmers; a metaphor for Frank Sobotka's inability to extricate himself from the smuggling operation despite his desire to.

Vondas makes this comment as a veiled criticism of Frank's caution in pursuing further deals with The Greeks' organization when faced with a police investigation. The season's theme of industrial decay is also thereby continued.

Although credited, Frankie Faison and Deirdre Lovejoy do not appear in this episode.

Colonel William Rawls questions detectives Lester Freamon and Bunk Moreland about their case. He tells Freamon he has been detailed to the Southeastern district and recommends that Bunk bring in a fresh detective.

Bunk, Beadie Russell, Ray Cole and Mackey serve grand jury summons on checkers at Frank Sobotka's union who worked on the Atlantic Light, the ship that delivered the container that the dead girls were found in, including Johnny "Fifty" Spamanto and Thomas "Horseface" Pakusa. Sobotka is enraged that the detectives believe he knew anything about the girls.

The grand jury prosecutor informs Bunk that the hearings brought little information. Out of options, Bunk quizzes Russell about informants in the docks and is disappointed when she has none. Later, Russell visits an old flame in Sobotka’s union named Maui. She sounds him out about becoming an informant while he tries to reinitiate their relationship. He refuses to give her information on his fellow union men but offers a tip – the union computers may be useful in tracking containers.

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