Since his father died and mother went into a mental asylum, schoolboy William lives poorly but relatively happily with his dodgy 'retired' maternal uncle Nils, a small fry crook who fences and so on. Both need cash, William to pay off bully Martin and Nils to pay Bertil Brystkasse's gang the money he lost gambling. William earns a reprieve by dog-walking Bertil's guard dog, but Nils isn't earning nearly enough to make that deadline and decides to stake it all on the horse races, expecting 'lucky' William to pick the right winner, with neither informed, so the kid goes by a mysterious advice his mother wrote down at their last visit.