- You may be looking for the real world novelisation.
Doctor Who and the Arc of Infinity was a book depicting the series events of when the Fifth Doctor and Nyssa reunited with Tegan in Amsterdam, and then had a "dreadful affair" with Omega trying to take over the Doctor's body. It was set after Doctor Who's Time Flight, when the Fifth Doctor left Tegan at Heathrow Airport, and Doctor Who and the Land of the Dead, though that hadn't always been the case. (PROSE: Bafflement and Devotion)
Behind the scenes
This is a in-universe counterpart of the real world Target Books novelisation Arc of Infinity that exists within the Doctor's universe. It was referenced as a fictional citation in Bafflement and Devotion.
While the title in the real world is simply "Arc of Infinity", the title provided in Bafflement and Devotion is a play on the titles of older Target Novelisations, which often placed Doctor Who and the at the beginning of the title.