Directed by Raymond De Felitta; screenplay by Paul Reiser

Starring Peter Falk and Paul Reiser, with Elizabeth Perkins, Olympia Dukakis, Ann Dowd, Claire Beckman and Mimi Lieber

Rated PG-13; 96 minutes

How great an actor is Peter Falk? He’s so great that he makes Paul Reiser look like a good actor simply by sharing a scene with him.

No, that’s unfair. Reiser is not so much a bad actor as a bland one, with a tendency to be cast as an ordinary-looking guy who can be extraordinarily annoying (Diner) or astonishingly weaselly (Aliens). But memorable or not, he almost always makes his co-stars look good. Even when he graduated to leading man, on the TV series “Mad About You,” (which he co-created), his crack comedian’s timing helped make Helen Hunt a multiple-Emmy-winning comedic actress. (Hunt may want to give Reiser a call; her career has been less than stellar since winning the Oscar).

Reiser’s ability to play to his fellow actors’ strengths is doubly demonstrated in The Thing About My Folks, which Reiser wrote with Falk in mind. It’s a touching film that has to overcome a plot that smacks of contrivance: Falk’s Sam Kleinman drops in on son Ben (Reiser) and his wife Rachel (Elizabeth Perkins) with the news that Muriel, his wife of 40-plus years, has left him, leaving only a note that was seemingly cribbed from a few dozen Lifetime TV movies. To help get his mind off his troubles, son takes father on a brief road trip that stretches over several days, giving them an opportunity to “bond,” rake up old grievances and do a bunch of movie-road-trippy things (pick up a cute mother/daughter couple, get in a bar fight, buy a classic car, etc.).

But if the situation is a too-pat setup, the execution is anything but, mostly due to Falk’s incredible ability to fully inhabit his characters while still remaining blissfully, gloriously himself. How does he do that? And why does it seem right that Peter Falk always seems to play “Peter Falk,” while people blame stand-up comedians like Paul Reiser for always playing themselves?

One reason may be that Falk never condescends to the material. He plays the at first bewildered, then angry, then accepting husband/father like a combination Falstaff/King Lear, but without a trace of actorly hamminess. When Reiser confronts him with evidence that may explain why Falk’s wife has finally left him now (a never-sent letter the mom wrote long ago, detailing Falk’s callousness and obsession with business), Falk’s anger and incredulity seem right on target.

Falk has perfected the ability to seem real in the most unreal situations: part of the humor of his funniest film, The In-Laws, is that his rogue CIA agent seems like a real person despite behavior that only gets weirder as the film goes on. As Alan Arkin did in that film, Reiser’s ordinary-guyness grounds Falk, making even their most banal conversations seem plausible.

Credit should also go to Reiser as author of the screenplay, which artfully uses the situations as a means to explore both characters’ psyches. (Reiser has been convinced for so long that his father was the bad guy in the marriage that it has shaped — or warped — his own marriage and fatherhood.) There’s nothing that remarkable about these insights, but they are no less true for that. Director Raymond De Felitta respects the text and gives the actors breathing room, maintaining an unhurried pace as father and son shift perspectives a bit at a time.

Falk is so good, and is so central to the film’s strength, that The Thing About My Folks almost falls apart in its final 10 minutes, when the focus shifts to Olympia Dukakis’ Muriel and the real reason for her sudden departure. First of all, Dukakis doesn’t seem at all like the person Falk and Reiser have been discussing all through the movie. This could be a commentary on the ways family members lock others into their childhood perceptions of them, refusing to notice that time changes us all — even our mommies. Mostly though it’s just confusing, as the sad, angry woman Falk and Reiser had described is personified by a wise, resigned Dukakis.

In addition, Reiser’s desire to tie up every emotional loose end seems too clean and neat, as if the final commercial break was approaching. But if the ending is too tidy, it doesn’t erase the funny, insightful, messy humanity of the bulk of the film.