Marvin’s Room, Raven Theatre. Inaugurating its spanking new home with a hometown drama that made it big, Raven Theatre presents Scott McPherson’s story of huge-hearted spinster-saint Bessie, who lives to love. Just as pointlessly as McPherson was hit by AIDS, she’s stricken with leukemia. Her need for a bone-marrow transplant triggers a reconciliation with her slatternly sister Lee, who’s been a stranger for 20 years, and Lee’s troubled teenage son, Hank, a part-time arsonist who must learn that virtue can be its own reward. Seldom has a play sought so much good from inexplicable misfortune.

The play’s appeal lies in its tricky balance between soap-opera sentimentality (think Terms of Endearment) and unflinching depiction of the human body as a sick joke. Though Bessie is falling apart, she feels “so lucky to have loved” (but, significantly, not to be loved). Fortunately, in Michael Menendian’s staging the gallows humor of McPherson’s medical burlesque never loses the pain behind the laughs.

As earthy, controlling Lee, Liz Fletcher delivers a dynamo who can finally run toward rather than away from something. Jeremy Glickstein’s Hank (remarkably resembling the late playwright) complicates adolescent surliness with an astonished vulnerability. Esther McCormick has twinkly fun as an irascible invalid. Holding them all together is JoAnn Montemurro, a more stolid Bessie than her predecessors. The character’s endurance shines through, but Montemurro’s dourness undermines the gratitude.