It starts to rain and when they finally go to open the door it won't budge. Everything they try fails including smashing a window, it's like the rain won't let them leave.
They settle in and start exchanging messages with their neighbours but nobody has any telephone or Internet service so they've no idea what's going on.
Days turn to weeks and they start to realise there's something in the rain.
What an oddity. This starts off like a cosy lockdown allegory, starts to veer towards the Donner Party, realises nobody has the stomach for that and goes for Earth Abides with them managing to do subsistence farming and a little animal trapping in a way that seems pretty damn improbable. Then the final act is survival horror.
Excellent performances from Lee and Moura can't save a messy movie that totally bottles the ending and goes for the weak sauce 4/10.
I also must comment that the writer must have read Kraken by China Mieville. If you watch it you'll know what I mean.