Set in Cornwall, deals with the successful efforts of two small cousins to frustrate the machinations of a pair of villains in search of a special ore in a deserted tin mine. Serial, consisting of 8 episodes: 1. Secret agent (15mins; 1390 feet) 2. Danger in the dark (18mins; 1577 feet) 3. Trapped underground (15mins; 1345 feet) 4. Poison gas (14mins; 1256 feet) 5. Sudden peril (17mins; 1547 feet) 6. Hot on the trail (16mins; 1478 feet) 7. Out of control (16mins; 1423 feet) 8. Desperate finish (17mins; 1561 feet)