Rosamund Pike wears an unidentified watch

In the big family group shot, wedged onto a sitting-room sofa with three children fanned around her, Rosamund Pike's Abi wears a soft denim shirt-dress and a small pale watch: a round case on a thin light strap. Abi and her husband Doug, played by David Tennant, have separated. They have driven the children up to the Scottish Highlands and agreed to pose as a couple for the 75th birthday of Doug's father Gordie, played by Billy Connolly, who has terminal cancer and a few months left.

Andy Hamilton and Guy Jenkin wrote and directed the 2014 film, working in the vein of their BBC sitcom Outnumbered, which made its name letting child actors improvise the adults into corners. The same engine runs here. The McLeod children answer every grown-up question with ruinous honesty and cannot keep the marriage secret for long. The watch gives away even less than they do: the camera never settles on it, and no dial detail or logo resolves. In a house where the children will repeat anything, the plain watch on the wrist of the woman keeping the biggest secret is the one thing on screen no one can read.

What the trip is really for arrives on a beach. Gordie, who has told the children he is descended from Vikings, dies there while the adults are caught up in their own fight back at the house, and the children, using fuel from his pickup, send him out to sea aflame on an improvised raft, the Viking burial he had asked them for.