A group of schoolboys become entangled in the activities of a group of smugglers (including two wanted fugitives from Malaysia).
Siblings Pippa, Alan, and Lynne Dawson and their friends Mick and Rob are staying in a Sydney boarding house. While swimming one day, they save an injured English boy from drowning, and hear footsteps running away. While they decided what to do, they take him to recover in their boarding house. The boy proves to have amnesia, and the Dawson family take him to their home at Wallaby Hill. Subsequent adventures include Tim winning a game of rugby for Alan's team (despite not being able to remember if he'd ever played before), attacks on Tim in the street, an abduction by Tim's 'Uncle Albert', Tim running away to keep his friends safe and finding work on an outback farm, a reuniting with the Dawsons, the recovery of Tim's memory after he is deliberately kicked in the head during an important rugby game, embezzlement, and the final confrontation with the would-be assassins, whom 'Tim' lets go after making them promise that they will become good citizens.