Here is Lou, a film produced by Bad Robot for Netflix. It has an irresistible premise, which is basically to make a Liam Neeson grumbling action thriller only to replace Neeson with award-winning and much-loved dramatic actress Allison Janney (The West Wing, I Tonya). Janney does a tremendous job too, immediately forging a gritty, miserable, and fascinating protagonist. Had the film stuck to its original set-up – suicidal bruiser with a shady past helps rescue her neighbour’s kidnapped daughter – Lou would be a creditable, stripped-back addition to the action genre. Sadly Maggie Cohn and Jack Stanley’s screenplay tries to complicate things with surprise turns and extensive back story; the more they fiddle with the basics, the worse Lou gets. It’s a fun movie, until it isn’t.

It makes this sort of film so frustrating to watch, because the ingredients for an enjoyable thrill ride are all set up wonderfully. That it all stumbles and falls apart at the midpoint suggests a production that failed to trust the material. Janney is excellent as Lou, and makes a refreshing change to all of the grizzled male ex-soldiers that usually populate the genre. She represents a trick forged by the likes of Don Simpson and Jerry Bruckheimer, who worked out back in the 1990s that they could make a fortune casting respected dramatic players like Nicolas Cage and John Cusack as action stars. Quite frankly Janney is a gift, and Lou wastes her.

The film does not skimp on acting talent elsewhere. Jurnee Smollett is great as Hannah Dawson, whose daughter Vee (Ridley Bateman) is kidnapped by an estranged – and presumed dead – abusive husband. Initially placed as a sidekick to Janney, she manages to develop a strong, relatable character who works well within the hunter-vs-hunted setup. Logan Marshall-Green struggles, on the other hand. It is no criticism of his talent as an actor; he simply cannot make anything very sensible out of the backstory and character development he is given.

Anna Foerster directs the film serviceably, in a straight-forward, no-nonsense fashion that works well in the first half. It seems a better match for her style than her 2016 debut Underworld: Blood Wars. In the end, however, it is the screenplay that ruins everything.

When Lou begins, it uses implied and unspoken back story to give atmosphere and depth. Hannah and Lou have a contentious relationship, and when Vee is taken during a thunderstorm Hannah has no chance but to rely on Lou for help. As Lou progressively demonstrates a talent for tracking, hand-to-hand combat, survival skills, and firearms, it builds a tremendous amount of enjoyment. Who is this woman? Where did she learn such skills? Kept vague and anonymous, and it just adds much-needed texture to a simple story. The moment Lou’s origins are revealed, that frisson immediately evaporates. The moment those origins are used to tie every seemingly unrelated aspect together, something tight and simple becomes unconvincing and convoluted.

I had big hopes for Lou. I have an enormous fondness for Allison Janney. Sadly this is a massive disappointment.