Doug (David Tennant) and Abi (Rosamund Pike) are in the process of dissolving their marriage. They seemingly can’t stand each other, frequently getting into contentious shouting matches, but they agree to put on airs that things are okay for the sake of attending the 75th birthday party of Doug’s ailing and not long for this world former soccer star father (Billy Connolly). With their three children in tow – only one of whom knows of their impending divorce – and Doug’s micromanaging, overprotective brother (Ben Miller) turning the entire weekend into an overblown extravaganza, the couple has to try extra hard to keep their lies quiet so no one gets upset.

A dark comedy of manners and errors, What We Did on Our Holiday is a hard film to talk about in terms of why it ultimately fails because it requires giving away a plot twist to describe how it squanders so much early potential. It almost works up enough goodwill to overcome its own dreadful third act, but that oddly just makes the heinous conclusion all the more intolerable. What’s worse is that the aforementioned twist is a pretty easy one to spot, and one that’s cleverly handled from a comedic perspective. It’s everything that comes after the twist that will leave viewers unnecessarily slapping their foreheads in disbelief.

While Tennant and Pike are ostensibly the headliners and are great at playing petulant, petty prats that have lost sight of how to conduct themselves as adults, the real stars here are Connolly and the children. While Connolly brings a large amount of warmth (and the film’s biggest laugh out loud turn of a phrase), it’s youngsters Emilia Jones (playing the studious and honest eldest), Bobby Smallridge (as the viking obsessed son), and Harriet Turnbull (as the youngest, whose best friends are rocks) that shine the brightest. Veteran TV writer/directors Andy Hamilton and Guy Jenkin wisely ground the film’s first hour from the perspective of the kids, giving them the funniest lines and allowing the trio to showcase some impeccable comedic chops.

But then comes the twist and the story shifts focus squarely to the older characters and a wealth of subplots one forgets the film has been quietly accumulating. It becomes an unwieldy mess seemingly only so Tennant, Pike, and Miller have something to do. One wishes they didn’t because the film reaches an obviously satisfactory point of escalation and conclusion just about an hour in. The final result is a third act that races to the end with no less than half a dozen subplots, while forgetting about three or four others involving characters that can be cut from the film entirely.

It all leads to a maddeningly contrived and far too neat conclusion that feels completely unearned. If the film ended about an hour earlier and actually reduced the roles of its two biggest stars to cameos, What We Did on Our Holiday would have been pretty great.