Virgin Missing Adventures
From Tardis Wiki, the free Doctor Who reference
Following the success of the New Adventures series based on the Seventh Doctor and his companions from Survival onwards, Virgin Books began a series Virgin Missing Adventures. These featured the adventures of the first six incarnations of the Doctor.
The first Missing Adventure served as a sequel (and also prequel, from the Doctor's point of view) to the New Adventure novel Blood Harvest, in an obvious ploy to get readers to buy both books. The Missing Adventure, Cold Fusion featured a direct crossover in the form of the Fifth meeting the Seventh Doctor, Roz and Chris Cwej from the New Adventures books.