A nice guy does a not-very-nice thing in Tom McCarthy‘s Win Win. It’s financial desperation that nudges New Jersey lawyer and wrestling coach Mike Flaherty (Paul Giamatti) into doing the unthinkable: becoming the legal guardian, for $1,500 a month, of a client (Burt Young) who’s suffering from dementia.

Mike argues to the judge that he’ll be able to keep the old man in his own home, as he desires. But when everything gets OK’d, Mike just dumps the guy into the same retirement facility the state was going to order him into. Things get complicated when the man’s teenage grandson (Alex Schaffer) shows up, having run away from his drug-addled mother. But when the sweet if monosyllabic kid turns out to be a champion wrestler, Mike sees another plus to having taken on such responsibility. Of course, the consequences of his choices aren’t as gilded as they promise to be.

Giamatti is as likable as he’s ever been as the good-natured but slightly devious Mike, aided by an entertaining supporting cast that includes Amy Ryan as his no-bullshit wife, Bobby Cannavale as his goofy best friend, and Jeffrey Tambor as an eye-rolling fellow lawyer/wrestling coach. McCarthy, auteur of The Visitor and The Station Agent, laces his smart drama with a fair dose of humor without it ever seeming forced. (Even the couple’s little girl, played by Clare Foley, is funny without being movie-cutesy.)

Underlying the begging-to-be-wacky circumstances is, most prominently, the theme of family—-specifically, the ones we’re born into versus the ones we create, whether they include friends, co-workers, or strange teens who appear at our door. In the end, selfishness turns into selflessness. Predictable, yes. But engrossing nonetheless.