There’s a touch of the old Twilight Zone to this unusual entry into the canon of apocalypse survival movies.

And what an apocalypse it’s been. There are only two survivors: scientist Ray (played by Sterling K. Brown) and former US President Billy (Mark Duplass). Best buddies since elementary school, they live in a self-sustaining dome of Ray’s own making, spending their days jogging in circles, playing Super Mario Bros and bickering.

Billy chides Ray for his taste in books (Manuel Puig’s Kiss of the Spiderwoman is going right over his head). Meanwhile, Ray harbours understandable resentments to do with the fact that Billy – an undistinguished POTUS, to say the least – was responsible for destroying humankind.

But all seems to be going OK, considering … that is, until the last female in the Biosphere’s fish farm dies. No female means no reproduction. No reproduction means no more fish protein – and that spells the end for Ray, Billy and homo sapiens as a species.

Then something remarkable happens. One of the surviving male fish transforms itself into a female. Under the threat of extinction, Nature has found a way.

Ray and Billy are understandably jubilant … and to reveal anything more at this point...