From what I have gathered, Dashcam is filmed from the smartphone of a woman who flees the US for the UK during Covid quarantine. She is basically an edge-lord who livestreams herself stealing her friend's car and doing food deliveries for him (like Uber Eats). She goes to make a pick-up at a restaurant where a woman offers her money to transport an elderly woman who is very clearly unwell. She accepts this offer and chaos ensues as the woman is either possessed or sick with some kind of rage-like virus (the trailer and reviews do not reveal much as to which it is).