A hair-raising mystery of the pulp variety for boys. ""Buck"" Brown, whose father is in command of an experimental unit helps uncover some serious sabotage against England's military secrets -- this time the gadget is a space ship. A foreign secret agent, masquerading as Professor Muldoon, and his gang dig tunnels and with the help of acid flame spirit the space ship to a secret hide out. However, Muldoon runs afoul of Wing Commander Peregrine, nicknamed the Blue Falcon, (""hard and chilled as tempered steel"") and all the tunnels and acid go for naught.