Set in Sheffield. Ted is suspected of stealing a new secret alloy, which has been sold to a foreign agent, from the steel works where he works. Don and Jane, Ted's brother and sister, suspect McCarthy, who goes abroad with the racing pigeons they help to look after. They follow him and recover the alloy. McCarthy corners them but they attach the alloy to Sir Galahad, the fastest of the pigeons, who flies back home. A chase ensues by aeroplane and train, finally arriving back at the steel works. McCarthy is captured and Ted's name is cleared.