[Illustration: fourth instalment]
BY PERCY F. WESTERMAN
GERALD TREGARTHEN, sub-lieutenant of H.M.S. Calder, being on leave, sails from Poole with his old school chum Jack Stockton on board the latter's yacht Playmate. In mid-Channel the yacht is run down; the two friends are rescued, and find themselves on board a mysterious cruiser—the Olive Branch—commanded by Captain Brookes. Finding that Tregarthen is a British naval officer, Captain Brookes announces his intention of keeping him on board, and, after due deliberation, Gerald decides to fall in with the captain's plans, as far as his sense of loyalty will permit.
Tregarthen is initiated into the secrets of the Olive Branch, including that of the deadly ZZ-rays—an irresistible charge of electricity whereby the destruction of a hostile ship can be made at will. Captain Brookes also explains that by the power at his command he hopes to make war so terrible that no nation will venture to declare war; thus universal peace will be assured.
During the voyage south Schneider, the ship's scientist, deserts, taking with him some important plans. He is found on board a German "tramp," and is brought back to the Olive Branch, which when this action is reported is branded as a pirate.
Hostilities break out between Chili and Peru, and Captain Brookes determines to intervene. The Olive Branch is damaged by a mine, and puts into a Chilian harbour for repairs; but while in dock it is trapped by a British squadron demanding its surrender by daybreak. Captain Brookes is handicapped by a vow never to fire on a British vessel. At midnight when the damage to his ship has been repaired, he makes use of his Z-rays to extinguish the searchlights of the British squadron. Then the Olive Branch starts forward at full speed.