Based on the greatest heist in British history, small-time crook Terry Leather takes on a bank heist when an old friend offers him an inside track to the vault. Along with his hastily assembled team of low-rung criminals, Terry finds himself the target of ruthless mobsters, the police, government officials at the highest level, and even the royal family.

Roddy is a decidedly upper-crust "society mouse" who lives the life of a pampered pet in a posh Kensington flat. When a sewer rat named Sid comes out of the sink, he desides he had hit the jackpot. Roddy schemes to rid himself of Sid by luring him into the "whirlpool." Sid may be an ignorant slob, but he's no fool, but it is Roddy who winds up being flushed away into the bustling sewer world of Ratropolis. There Roddy meets Rita, an enterprising scavenger...