Espionage comedy is so-so, but Kate McKinnon? So good.

“The Spy Who Dumped Me” gets by, barely, thanks mainly to Kate McKinnon. Her crazily fluid and unpredictable comic timing, and her willingness to go big — well past Madeline Kahn-big and very near Eddie Cantor-big — has saved several movies. She salvaged the “Ghostbusters” reboot, rescued parts of “Rough Night” and wrung what she could out of the damp rag “Office Christmas Party.” Working with a game Mila Kunis, McKinnon takes care of this one, too, whether with some screwy verbal aside or pulling a pop-eyed, slack-jawed, weirdly delighted reaction.

Usually the plot’s up to people getting impaled, or kicked in the face, or tortured by sinister enemy gymnasts. Co-writer/director Susanna Fogel’s action comedy about best friends caught up in international espionage is stupidly, relentlessly violent. This makes it hard for the audience to relax and enjoy. Yet McKinnon’s apparent improvisations and inventions create a second, better movie in the margins.

Seriously: Why have action comedies turned into a series of grisly “kills” barely making room for the “comedy” part? The influences go back a generation or two, when the first “Beverly Hills Cop” or “48 Hrs.” came out. Those films were really sharp; the mixtures worked, though it took “Beverly Hills Cop” one sequel to screw it up.

More recently, and more pertinent to the blueprints used for “The Spy Who Dumped Me,” the Melissa McCarthy vehicle “Spy” clicked despite an overreliance on mayhem. (Killing’s easier than wit, and a more reliable ingredient for international box office.) In the McCarthy movie, we got a hugely funny accidental-shooting sight gag in the first minute, the setup bouncing off the tropes and conventions of Bond/Bourne/“Mission: Impossible.” It takes “The Spy Who Dumped Me” far longer to get going.

Fogel’s script, co-written by David Iserson, starts with Audrey (Kunis), a clerk at a Trader Joe’s-type store, smarting over a breakup text she’s gotten from boyfriend Drew (Justin Theroux). Allegedly the host of an NPR podcast, in reality he’s a CIA agent in possession of a flash drive full of dangerous information. Others want it, and when Drew shows up at Audrey’s apartment, with killers on his tail, “The Spy Who Dumped Me” ropes Audrey and pal Morgan, played by McKinnon, into the chase to Vienna, Paris, Prague and environs.

You could do worse than that premise, and McKinnon and Kunis bring a can-do spirit to the material. Sam Heughan’s charming British agent presents a love interest for Audrey. Ace character man Fred Melamed pops in as a smooth, cultured friend of Audrey’s father (Paul Reiser), enticed by Morgan, though he’s barking up the wrong tree. But promising bits, such as McKinnon infiltrating a Cirque du Soleil-style show and trying to fake her way through it, go nowhere. And somewhere around the 40th act of brutality, played straight, I just wanted McKinnon to chase a better movie. See this one for what’s going on in the margins.