Holliday Grainger and Tom Burke are excellent again as detectives on the tail of a killer. But given the impenetrable source material and workaday plot, it’s shrug-worthy TV at best

Is Robin Ellacott in love with Cormoran Strike? “I definitely don’t want to be,” says Robin (Holliday Grainger) of her friend and private-investigator business partner. “That’d screw everything up.” In the sixth season of Strike, a crime drama based on the sixth Strike novel by Robert Galbraith, AKA JK Rowling, it feels more than ever as though the show itself is afraid that this is true. Grainger and Tom Burke, who plays the titular Strike, do a lovely line in will-they-won’t-they romance, but the series might expire if that ever resolved itself, because the sleuthing part of it is moribund already.

As a work of crime fiction, the TV version of Strike is several removes from having a compelling reason to exist. It is based on a series of hit novels – fine, nearly all detective dramas are – but these books aren’t especially well regarded. They surely attract as many sales and comment pieces as they do only because their author created Harry Potter. That is no help for a TV show trying to succeed on its own terms.