Tim Bayliss (Kyle Secor) was the rookie during Homicide痴 first season. By the fourth, he's an experienced vet with a bad back (a degenerative disc, to be precise). Stan Bolander (Ned Beatty) and Beau Felton (Daniel Baldwin) are gone, leaving Meldrick Lewis (Clark Johnson) and Kay Howard (Melissa Leo) without partners. Someone needs to come along to shake things up. Enter brash detective Mike Kellerman (Reed Diamond) from the arson unit. After impressing Lieutenant Giardello (Yaphet Kotto) with his sly interrogation of a shifty arson suspect in "Fire (Part One)," he痴 invited to join Maryland's finest. The loquacious Lewis, on his own since the third-season departure of Steve Crosetti (Jon Polito), has finally found the perfect sparring partner, while Kellerman would add some redheaded sex appeal to the acclaimed drama (hey, it worked for NYPD Blue).

Another new character, naive crime-scene videographer James Brodie (Max Perlich), makes his (somewhat shambolic) entrance in "Autofocus." All the other old favorites are back: Frank Pembleton (Andre Braugher) and wife Mary (Braugher痴 real-life spouse Ami Brabson), for instance, are expecting a baby, and the much-married John Munch (Richard Beltzer) is dating the new medical examiner. Interesting developments are in store for the rest of the unit, as well, including a change in location (due to a gas leak) and command (Howard is promoted, but Isabella Hofman's Captain Russert is demoted).

Notable episodes include "A Doll's Eyes," a look at a murder case from the perspective of the victim's family (with Oscar winner Marcia Gay Harden); "Heartbeat," inspired by Edgar Allen Poe's "Tell-Tale Heart"; and "Thrill of the Kill," an eerie tale about a spree killer with a split personality. And keep an eye out for those always-surprising cameos, like Jay Leno in "Sniper (Part One)" and Reverend Horton Heat in "Full Moon." --Kathleen C. Fennessy