It is pretty gripping stuff.

Away from the relay scenes, the film is rather conventional, but when Sarah and Ash — or rather his proxies — are on the blower, it’s enthralling stuff.

Even if it does eventually crumble to pieces, it’s a really strong thriller for the large majority of its runtime.

The action scenes are high-energy and pulse-pounding as the stakes evolve, even if the film’s climax twists the knife in a way that doesn’t feel quite right.