BBC Childrens Books published this Doctor Who adventure by Richard Dinnick in 2011. It features the Eleventh Doctor, Amy Pond and also Rory Williams.
The Doctor has to take Amy and Rory to the Tower of London until yet again the TARDIS lands them on a space ship called The Cosmic Rover. A space ship in the future is not quite the same as the only remaining Norman fort in present day London.
The crew of The Cosmic Rover have been sent from the planet Earth to explore the distant world of Hydron, which is almost entirely covered in water except for a few scattered tiny islands. The Cosmic Rover is supposed to be on a scientific voyage yet the Doctor suspects that something is a wry. Perhaps Rory has hit the nail right on the head when he states that there are far too many security guards for a simple exploration mission.
Unbeknown to Captain Jane Clancy there had been an expedition to Hydron the previous year when all but two of the people that went on it were killed in fighting with the native fish people of the planet. The Head of Security Fleming and Doctor Morton were those survivors, and they returned to steal a valuable source of energy. However the fish people recognise the submarine The Ocean Exploer as being human and put a virus on board to weaken the crew.
The Doctor and Amy leave Rory on board to look after the sick whilst they attempt to contact the fish people to assure them that the humans mean them no harm, except for the greedy Fleming that is. The Doctor learns how to communicate with them yet as usual has a tight time scale to match in order to avert disaster.