John Prentice is an officer in British Naval Intelligence.
When we first meet him, he is attached to the Signal Corps and happy there. He has intentions of, nor even any thoughts of, moving from that specialty into the intelligence business but he will find himself pulled along, a little at a time, by his friend, Peter Browning, who is very much a part of the clandestine department that a Sir Edward Trelawny of the Briths Foreign Office commands.
Our initial encounter with Prentice will take place at the midway point of the Second World War when he is stationed in Freetown, Sierra Leone, on the west coast of Africa, at the time still very much a colony of the British Empire. It is there that Prentice will begin his unofficial working with Browning. [It would not be wrong to consider Browning being the main player in the activities. Prentice plays a major role in all of the adventures but the first couple clearly has him being more of a co-star. This will change over time.]
While it would not be fair to say that Prentice was a 'womanizer', there is no doubt that his "fresh, young face" with its handsome features and his "fair, wavy hair" was a perpetual lure for the opposite sex and Prentice is far too much a gentleman to leave such lovelies abandoned. He gets a good amount of teasing about his apparently large number of acquaintances who are ever ready to spend time with him. He explains his seeming reluctance to marry any of them with the comment that "a few girl friends have the advantage of costing little or nothing while one's away at sea. A wife must be a permanent drain on the exchequer".
Playing a vital part in all but the first adventure is the lovely, impressive Tania Maitland, actress and singer and star of several traveling shows. She will get pulled into danger on more than one occasion but will also prove extremely useful in investigations which will help resolve matters. She is first courted by young Prentice but finds him a tad too immature at first; her eye will land on his older friend Browning and they will eventually marry.
[Spy fiction authority Barry Van Tilburg states in his comments on this series in The Mystery Fancier (Vol 7. Nr. 4 - July 1983) that "After Browning's death, John and Tania enter into two adventures of their own. Later, Prentice becomes a full Commander and marries Tania".]