Jack Havock was a space pirate in command of the good ship Sophronia. He was around sixteen whan he met Art and Myrtle Mumby on the Moon. Jack's parents were among the first settlers on Venus, and were changed into trees when the Venusian Changeling Trees spred their spores. Jack was was the only settler not to become a Changeling Tree and was found and brought to the Royal Xenological Institute in London. There he befriended Nipper, an amiable giant crab and Dr Ptarmigan, an RXI professor.