From oddly spelled title to botched finale, this ill-conceived bid to reboot the Terminator franchise is a baffling, goodwill-crushing mess. Yes, Arnold Schwarzenegger is back, but the terrifying figure of James Cameron’s 1984 cult classic has been reduced in Terminator: Genisys to a self-mocking, avuncular presence whose creaky catchphrase is now ‘I’m old, not obsolete’.

Striving to avoid obsolescence themselves, the film’s creators have come up with the notion of fractured timelines in order to extend the saga’s narrative and to get around the awkward fact that, as far as the viewer is concerned, the apocalyptic futures conceived by the previous movies are now all in the past.

So when resistance leader John Connor (here Jason Clarke) sends buddy Kyle Reese (Jai Courtney) from the future to 1984 Los Angeles to prevent a cyborg assassin from killing his mum, Sarah Connor (Game of Thrones’ Emilia Clarke), she is no longer a distressed damsel in need of rescue (as in Cameron’s original) but a ballsy kick-ass heroine who already knows about the threat from artificial intelligence Skynet and has spent her young life readying herself to meet it.

This time, Schwarzenegger’s Terminator is benign, goes by the cuddly nickname ‘Pops’ and is Sarah’s protector, and it is an all-embracing operating system, destined to be launched in 2017 (and personified by former Doctor Who Matt Smith), that is the menace facing humanity.

The plot is so head-spinning that we really do need the light relief provided by the string of self-mocking quips given to Arnie’s Pops. ‘I lack the mimetic skills to appear as anyone else,’ is a typical line. By contrast, his co-stars, the feisty Clarke excepted, don’t fare so well, and Clarke and Courtney’s performances are particularly grim and clunky.

Yet not everything about the film is a flop. The near shot-for-shot recreation of the sequence from the 1984 movie in which Schwarzenegger’s malign Terminator arrives naked from the future and encounters a trio of punks is cleverly done – although the Mohican sported by one of the punks now looks as quaintly old-fashioned as a periwig.

Certificate 12. Runtime 125 mins. Director Alan Taylor.

Terminator: Genisys is available on Blu-ray, DVD & On Demand from 2 November from Paramount Home Media Distribution.