Australian villains Colin MacGruder and Ray Stackpole return to London and steal a bus, posing as its crew. They rob an art dealer travelling on the bus of a Goya painting, which they plan to sell to a buyer in Amsterdam. Regan tracks them down by leaning on their accomplice, the dealer's female assistant, leading to a river chase and a shoot-out, making it the end of the line for the boys from Down Under.
