Mooney plays childish 25-year-old James who is obsessed with an amateurish children’s TV programme which chronicles the science-fiction adventures of a talking bear.

The show isn’t broadcast but arrives on VHS cassette to the bunker James shares with his oddly indulgent parents Ted (Luke Skywalker actor Mark Hamill) and April (Jane Adams).

James doesn’t think this is strange. After all, he’s never been outside due to the toxic air.

Then, about 10 minutes in, the FBI roll up – and they aren’t wearing gas masks. It turns out James was kidnapped as a baby and his real parents (Matt Walsh and Michaela Watkins) are waiting for him in non-toxic suburbia.

Worst of all, he discovers he is Brigsby’s only fan. The show was made by his kidnappers to indoctrinate him into life in the bunker.

As James struggles to adapt to life outside, he fi nds he just can’t shake off the bear.

Against the advice of his therapist (Claire Danes) and with the help of his snarky teenage sister Aubrey (Ryan Simpkins) he decides to tie up loose ends. Closure, if he needs it, will be achieved by shooting Brigsby Bear: The Movie.

This isn’t the first quirky indie film to extol the virtues of quirky indie-film-making but it manages to be sweet, surprising and consistently amusing.

Mooney has great comic-timing and is ably supported by a wonderful ensemble cast. Hamill is a revelation (a good sign for Star Wars fans who can see him in The Last Jedi from Friday) and when a kindly detective unearths his inner thespian, Greg Kinnear has a chance to show off his comic side.

It’s funny, clever, heartwarming and on the right side of the line that separates quirky from twee. These are the ingredients of a cult hit.