A fun but somewhat predictable single-location crime comedy. Put various unrelated parties into a single room, add cash, a corpse and confusion, and you have all the ingredients for a fun little crime flick. It's not a film that innovates on the formula, but the execution is certainly on point.
When a petty thief is raiding an apartment, two other people walk in who clearly don't belong there. After a scuffle the thief wakes up in the apartment, with a delivery boy who finds himself in a similar situation. Nobody knows what exactly is going on, but when they discover a load of cash in the freezer it's obvious that not everyone will walk out freely.
Performances are solid, the cinematography is nice enough and the intrigue is kept alive while the plot slowly unwraps. The conclusion is entertaining too. It's all good fun and there's nothing really wrong with Knock Knock, the only thing lacking is something that sets it apart from similar films.