Not excellent maybe, but by no means bogus either, this cheerful Bill & Ted threequel brings the story of our two laidback heroes up to the melancholy autumn of their middle age.

Alex Winter is Bill and Keanu Reeves is Ted. George Carlin, who played the boys’ cosmic time-travel guide Rufus in the first two films, died in 2008, and makes a virtual-reality appearance here courtesy of archive footage; Kristen Schaal plays his daughter, Kelly.

Nowadays, Bill and Ted are getting on in years, and their band, Wyld Stallyns, has suffered a cataclysmic loss of popularity. The apples of the men’s respective eyes are their music-mad 20 something daughters, each of whom has effectively been given the name of their dad’s best friend: Thea (Samara Weaving) and Billie (Brigette Lundy-Paine). This crossover further seals their friends-for-life dedication. Each young woman is of course weirdly similar to her old man, a single-joke mannerism that restricts these performers a fair bit.

The terrible crisis arrives when Bill and Ted are summoned into the distant future by Kelly, and informed by the universe’s Great Leader (an amusingly imperious Holland Taylor) that they have to compose a great track to bring the world together and prevent the destruction of space and time. The boys, sublimely confident that they can do it, but unwilling to go through the faff of actually doing it, simply decide to time-travel forward to the point when it has been done and snatch the composition from their future selves. But the Great Leader has an alternative plan to save the world, simply to kill Bill and Ted, for which she has trained a neurotic robot assassin called Dennis, channelling Douglas Adams’s Marvin the Paranoid Android – a nice turn from Anthony Carrigan.

Bill and Ted’s wacky adventures and bizarre encounters with their own variously transformed selves run in parallel with the attempts of Thea and Billie to assemble their own universe-saving supergroup on their dads’ behalf. They travel back to the 1960s and recruit Jimi Hendrix (DazMann Still), to the 1920s to pick up Louis Armstrong (Jeremiah Craft) and then to 18th-century Salzburg to enlist Mozart (Daniel Dorr).

It’s amiably amusing, and Bill and Ted’s Peter Pannish inability to accept the ageing process is enjoyably surreal, with a weird tinge of not-entirely-intentional tragedy. The failure to give Weaving and Lundy-Paine anything really funny to do is a problem; but all the cast are likable, and it’s a sweet-natured journey backwards and forwards down memory lane.