Fifteen-year-old Owen cultivates a tough-guy persona: He dresses in black, wears combat boots and sports a watch cap on his shaved head. DIY tattoos marble his body. But return him to the Nantucket seashore where he was born, and the kid becomes a fraidy-cat: Acutely averse to sand, he won’t take a step without laying down his black jacket as a beach-suppressing walkway. That droll image crops up early in Bob Bartlett’s “Swimming With Whales,” now in a world premiere run at 1st Stage. Affecting and inventive, if leisurely and occasionally over-deliberate, the play spins an almost novelistic narrative about loss, healing and courage in the face of death. Add the figure of a mysteriously lurking, seemingly empathetic, possibly ailing whale, and the story might sound as deep and daunting as the Mariana Trench. But local playwright Bartlett shrewdly lightens his material with touches that are funny yet revelatory of theme and character.

Director Alex Levy’s engaging production features compelling performers, including the excellent Ethan Miller as the initially glowering and foulmouthed Owen. A Boston resident who is in treatment for a serious illness, Owen has traveled unwillingly to the Nantucket home of his father, Patrick (Matthew R. Wilson, appealingly crotchety and hapless), whose lover has just died. In the 1960s, Patrick and his lover made up a tightknit, hedonistic foursome with Owen’s mother, Anne (a persuasive Teresa Castracane), and Grace (Jessica Lefkow, vivid and funny), who is now a local park ranger. But those days of counterculture bliss are gone, and any mention of them exacerbates Owen’s hostility to Patrick and the great outdoors. Or so it goes at first: Owen’s attitude, and his relationship to his father, change in ways that are predictable. And the play spends too much time emphasizing both the teenager’s initial sullenness and the fact that Patrick, Anne and Grace really, really love Nantucket.

But Bartlett (a founding member of local playwrights collective the Welders) largely steers the drama away from undue sentimentality, and he does a great job teasing out the significance of the ocean and the whale (Nate Shelton as Ketos) without letting either of those saltwater presences become ponderous symbols.

Kathryn Kawecki’s set — a rickety wooden cottage, stylized ocean and lots of sand — helps flesh out the story. Sarah O’Halloran’s sound design, rich in waves and whale song, is telling and atmospheric; and Debra Kim Sivigny’s costume design speaks valuably to character and state of mind. But the chief rewards of the production are the actors’ tangy interpretations of the script’s more piquant moments. The galled Patrick holding a dishrag to Owen’s upturned ­nostrils, after the kid has developed a nosebleed. The savvy Grace feeding pancakes to Owen, who strenuously objects to sharing her utensil. (“Is civilization down to its last fork?” he demands.) Owen, in the middle of a seizure, conversing in dreamtime with the cetacean. “Swimming With Whales” has longueurs and some overemphasis, but it also has moments that are more than seaworthy.

Swimming With Whales, by Bob Bartlett. Directed by Alex Levy; lighting design, Robbie Hayes; props design, Cindy Landrum Jacobs; assistant director, Rocky Nunzio. 2½ hours. Tickets: $15-$33. Through June 24 at 1st Stage, 1524 Spring Hill Rd., Tysons Corner.