Fans of Keegan-Michael Key and Jordan Peele’s eponymous sketch show will not be surprised to learn that their movie, “Keanu,” feels like a sketch — a funny one, sure, but less and less so the longer it goes on.

The basic comedic premise is solid, and let’s be clear on what that is. It’s that two ordinary men, Rell (Peele) and Clarence (Key), pretend to be hardcore gangstas in order to retrieve something stolen from Rell by a mid-level drug lord named Cheddar (Method Man). If it’s a one-joke movie (and it kind of is), that’s the one joke, these two fakers in over their heads among thugs.

The joke on top of that joke is that the stolen item is a kitten. Now, li’l Keanu is awfully adorable, and it’s not NOT funny to see grown men (especially violent criminals) cooing over a kitten. But the cat isn’t what drives the humor or the plot. Keanu is little more than a McGuffin — he could be a computer disk or a bag of money and the plot would barely change from the action-comedy template employed here. (The screenplay is credited to Peele and “K&P” TV show writer Alex Rubens. It was directed by the show’s Peter Atencio.)

No, the real thrust of the humor is timid househusband Clarence and irresponsible-but-generally-law-abiding Rell acting like tough, experienced drug slingers while making the rounds with Cheddar’s crew. Most of it works well enough. In one section, Rell and Hi-C (Tiffany Haddish) deliver drugs to a celebrity (Anna Faris) while Clarence waits in the van with the other three crew members (Jason Mitchell, Jamar Malachi Neighbors, and Darrell Britt-Gibson), introducing them to George Michael’s “Faith” album. (It holds up.)

These two being in over their heads is funny, but the returns on the gag diminish as it’s repeated without many new wrinkles being added. Yet it’s kept afloat by Key and Peele’s chemistry together and their skill at playing funny satirical versions of black stereotypes. As soon as they hit on an idea that will sustain itself for the length of a feature, I have no doubt they’ll make a hilarious movie.

B- (1 hr., 38 min.; R, abundant harsh profanity, some strip club nudity, action violence.)