Once again, we are reminded of the way that the US manages to defang, monetise and institutionalise its own initially thrilling subcultures.

Candid and clear-eyed, this doc will wow boarding fans but has something to offer to the unconverted too.

A sad, involving story.

The film loses momentum and focus by chasing too many threads. Ben and Tas are such fascinating characters – and truly tragic; this is also a tale of hubris – that the film’s divergence from their story is exasperating.