| Episode cast overview, first billed only: | |||
| Dominic West | ... | Det. James 'Jimmy' McNulty | |
| Reg E. Cathey | ... | Norman Wilson | |
| John Doman | ... | Acting Commissioner William A. Rawls | |
| Aidan Gillen | ... | Mayor Thomas 'Tommy' Carcetti | |
| Clark Johnson | ... | City Editor Augustus 'Gus' Haynes | |
| Deirdre Lovejoy | ... | Asst. State's Atty. Rhonda Pearlman | |
| Tom McCarthy | ... | Scott Templeton | |
| Clarke Peters | ... | Det. Lester Freamon | |
| Wendell Pierce | ... | Det. William 'Bunk' Moreland | |
| Lance Reddick | ... | Dep. Comm. for Operations Cedric Daniels | |
| Andre Royo | ... | Reginald 'Bubbles' Cousins | |
| Sonja Sohn | ... | Det. Shakima 'Kima' Greggs | |
| Seth Gilliam | ... | Sgt. Ellis Carver | |
| Domenick Lombardozzi | ... | Thomas 'Herc' Hauk | |
| Michael Kenneth Williams | ... | Omar Little (credit only) | |
After Marlo tells Levy the only people who knew their code were himself, Chris, Cheese and Monk Metcalf (Kwame Patterson), all of whom are in jail, Levy begins to dig into who exactly the police's CI is. Greggs tells Daniels that McNulty and Freamon made up the serial killer, and Daniels in turn tells Carcetti. However, fearing for his campaign for governor, Carcetti orders a cover-up, much to Daniels's disgust. As McNulty tries to talk the homicide department out of throwing more man-hours into the serial killer case, an unanticipated problem presents itself. Elsewhere, Freamon learns who the leak is at the courthouse, and Levy realises the Marlo investigation used an illegal wire, forcing Pearlman to negotiate. At The Sun, when Templeton tries to sneak his biggest fabrication yet into the paper, Haynes decides he has had enough. Meanwhile, Bubbles debates whether to let Fletcher publish his story, the hierarchies at the police department, City Hall and The Sun receive a shake-up, ... Written by Bertaut
A great series ended with a great episode. Hats off to the writer especially for writing this amazing series. It's called a TV novel for this reason. The way it dwells upon the viewers is fantabulous. The series was moving, gripping, cunning in it's own way. The slowness is its greatness. The finale is really really good. This is the best season of all times along with the sopranos, hats off. The pillars of TV