Through it all, Fontana and his collaborators (including guest director Steve Buscemi) maintain impressive focus on dozens of finely drawn characters. Laced with homosexual tension, jealousies, religious fervor, and threats of betrayal, the season's most compelling conflicts involve impulsive killer Ryan O'Reily (played with cagey menace by Dean Winters) and his brain-damaged half-brother Cyril (Scott William Winters); and the manipulative Keller (Christopher Meloni) and his prison lover Toby Beecher (Lee Tergesen), a lawyer and convicted murderer whose survival seems perpetually uncertain. Tenuous order is barely maintained by warden Glynn (Ernie Hudson) and Catholic counselor "Sister Pete" (Rita Moreno), but the bulk of Oz's fourth season is devoted to chaos, as shifting loyalties keep all prisoners (and all viewers) in a state of anxious anticipation. The criminal histories of many inmates are shown in flashback, and one death-row scenario (involving guest star Kathryn Erbe) reaches its inevitable conclusion. By the time episode 16 ends with a blazing inferno, you'll be wondering about the fate of Rev. Cloutier (Luke Perry) and anxious for the tumultuous events of season 5. (Commentary accompanies two episodes: Fontana and Moreno offer informative anecdotes on "You Bet Your Life," but the Fontana/Winters/Tergesen commentary on "Famous Last Words" is raucously undisciplined and for hardcore Oz fans only.)--Jeff Shannon