Twenty years previously, Robert 'Fish' Fishman (Rainn Wilson) was heavy rock band Vesuvius's drummer.
But, when Vesuvius were offered a support slot for Whitesnake on the condition that they ditch their drummer, Fish soon found himself packing his sticks.
Now, two decades on, he's been sacked from his dead-end job, ditched by his girlfriend and forced to move into his sister's attic.
However, he unexpectedly - and unwittingly - gets another bite at stardom while preparing for a one-off gig with his 18-year-old nephew Josh's (Matt Gadman) band.
The only place Fish can find to rehearse in is very stuffy and humid, so - because he's on his own - he chooses to play naked. But he doesn't realise he's being recorded. And when the film clip is posted on the web it goes viral...