In their everyday patrols, the police straddle the thin line between right and wrong.

Countless cop dramas have explored this trope, but none more successfully and grippingly than FX's "The Shield." In season four, embattled detective Vic Mackey (Michael Chiklis, "Fantastic Four") must finally face the consequences of his brutal brand of justice.

At the start of the season, Mackey finds his career in shambles. His precious Strike Team has been disassembled and he's under orders to dispense justice by the book. Captain David Aceveda (Benito Martinez, "Million Dollar Baby") has finally moved on to his post at Los Angeles City Council, leaving a gaping hole at the top of the Barn. While Mackey isn't exactly sad to see Aceveda go, his life is turned upside down by the arrival of the new captain - and it's not who everyone expects.

By going against the grain and shaking up the status quo, season four challenges viewers' preconceived notions about the show and its characters.

Detective Claudette Wyms (CCH Pounder, "Face/Off") could easily have been selected as the new captain, since she was Aceveda and the Chief's handpicked successor, and, as a plot device, it might have provided enough of a spark for most series. But "The Shield" took a different route. The creators brought in Glenn Close ("The Stepford Wives") to play Monica Rawling, the new captain - and she nearly steals the show from Chiklis, which is no small feat.

The giant shake-up plays out well. All the officers that viewers have come to know and love must adjust to new roles and relationships. But playing nice has never been Mackey's strong suit, and it's not long before he and Rawling come into conflict. As bad as the internal struggles of the Barn may be, they pale in comparison to the growing tensions in its patrolling district of Farmington.

Another new cast member, Anthony Anderson ("Hustle & Flow"), plays the "reformed" gang member Antwon Mitchell. Anderson turns in a surprisingly strong performance as a man whose actions are far less noble than they initially appear.

Season four takes the series and tips it onto its head. Most of the friendships and alliances in the Barn are completely inverted. Mackey and his trusted partner, Shane Vendrell (Walton Goggins, "The Bourne Identity"), find themselves at odds over Shane's connections to Antwon. Even the partnership between Claudette and Dutch (Jay Karnes, "The Next Best Thing") is put to the test when she thinks he has an illicit agreement with the D.A.

There's a reason for the abundance of buzz surrounding "The Shield." It's simply the most captivating cop show on television. In fact, it's the best police drama since "Homicide: Life On the Street" ended its run in 1998.

The DVD set does this remarkable season justice by providing insightful episode commentaries and riveting deleted scenes. These extra features only augment a show that's done what few other series have accomplished: keeping a good thing fresh and constantly improving.

The Shield

FX

Rating:

Show: 4 and 1/2 out of 5 stars

Special Features: 3 out of 5 stars