Cirrus@Austlit

'Dosvidonia, Neptune King is the 18th book in this series. This time the boys are entangled in the world of espionage when C of MI6 recruits them on a special mission to the USSR. In the year 1963, double agent Kim Philby was discovered working for British Intelligence. Before they could arrest him, he fled to Russia and compromised the British spy network. An informant in Moscow wants to defect and asks the British secret service for help. As an inducement she offers them a list naming all the Soviet spies resident in the UK and USA. Because Philby knows all their operatives they enlist Neptune and Shark to go over to escort Svetlana Roshevsky and her list back to England.

Unfortunately for them, they run into Boris Slovinski who recognizes Shark from the time Shark and his brother exposed him as a spy and had him run out of England. Arrested, tortured, with the threat of being shot as spies, their situation is desperate. Incacerated in the notorious Lubyanka prison, their future looks bleak. Will they be sent to Siberia? Will they get out alive? This is their most dangerous case ever and the stakes are high. Will they survive and make it home? Start reading and find out...' (Publication summary)