Vondie Curtis-Hall's corrosive film about two strung-out jazz musicians attempting to kick their heroin habit has some fascinating insights into that process but is thrown off course by its uncertain tone. Late rap idol Tupac Shakur and Tim Roth star as the musicians who decide to kick heroin after witnessing the overdose of a singer friend Thandie Newton. The director attempts to crossbreed a horrific vision of the lives of these two characters with a gallows humor about their predicament, but the dramatic scenes of suffering are so wrenching, and so well-played that laughter is often impossible. Much of the film is taken up with the characters' futile attempt to get help from various drug-treatment facilities, and their bizarre debate about whether they should stab each other in order to be admitted to a Detroit hospital drug program is a satiric high point. The surprise of the film is the charismatic performance of Shakur, who was murdered after the film was made. He and Roth have a terrific rapport, and for their work alone the film is worth seeing. But for anyone who has witnessed the ravages of heroin addiction, and the threat of violence that lurks in its shadow, the wisdom of introducing a comic note is at least debatable.