This is a great improvement over Johnston's last novel Collision Course (1964) but is still the sort of book that might best have been carried off in a short story. A nameless stowaway is discovered on a British ship pulling out of Piraeus, Greece. He can't be sent ashore because the Greek authorities won't permit it, so he becomes a sort of permanent passenger on a British ship in the Mediterranean. In fact, he may well not be allowed to disembark at the ship's final British port, because of technicalities. The stowaway, a 50-some year old fellow in rags, never speaks throughout the novel. This may seem as if the author were reaching for a minor classic featuring a symbolic central figure, but Johnston dissipates his mystery by telling us just enough background material to make the stowaway a stock character in a tale of intrigue. The British Secret Service is on the tail of a defecting Russian biologist who has discovered both a population-sterilizing virus and its antidote. Is the stowaway this very man? A secret agent arrives on board to interrogate or identify him, possibly. But the stowaway disembarks at Naples. Returned, he disappears aboard ship...The climax explains away about everything that would have given the story more meaning than melodrama, but it is a good/tale and a natural flick.