• It was the only multi-Doctor story involving televised Doctors ever told by Virgin Books. It involved the unusual pairing of the season 19 Fifth Doctor with the Seventh Doctor near the end of the Virgin New Adventures line.

• Originally intended to be published alongside the novel So Vile a Sin to emotionally leverage Roz Forrester's death in that book, delays on Sin meant that people who read the book on publication didn't see this intended aspect of the book.

• As a multi-Doctor story, its perspective was unusual. The Seventh Doctor was portrayed as largely disdainful of his earlier self's presence because of the dangers it presented. Though temporal paradoxes and other consequences (1/3)

of two Doctors meeting were touched upon in televised multi-Doctor stories, here they were more central. Moreover, the structure broke with the format of televised multi-Doctor stories, which held that the latest incarnation (2/3)

was the "current" Doctor and therefore the effective headlining "star" of the show. On balance, Fusion was a Fifth Doctor novel that happened to feature the Seventh, rather than a Seventh Doctor novel that used the Fifth. (3/3)

• This is the only instalment of the Virgin Missing Adventures in which the Seventh Doctor appears.

• The reasons that the Doctor seems to not remember meeting his future selves in other multi-Doctor stories are discussed. In most of the televised adventures, it is credited to the Blinovitch Limitation Effect.

• The Seventh Doctor remembers the events of the novel from the perspective of the Fifth Doctor and uses this knowledge against his younger self. This also occurs in the audio stories Peri and the Piscon Paradox (1/2)

and The Four Doctors and the television story Time Crash in which the Sixth, Eighth and Tenth Doctors respectively likewise remember the events portrayed from the point of view of their fifth incarnation. (2/2)

• The Seventh Doctor describes his fifth incarnation as being "bland" and "not even one of the good ones." This reflects the Sixth Doctor's low opinion of his immediate predecessor immediately after his regeneration as he told his companion Peri Brown (1/3)

that "he had a sort of feckless charm that simply wasn't [him]." (TV: The Twin Dilemma) The Eighth Doctor was more fond of his fifth incarnation than his two immediate predecessors. He once described him as "terribly polite." (AUDIO: The Four Doctors) (2/3)

By the time of his tenth incarnation, the Doctor expressed a fondness for his time as the Fifth Doctor. He looked upon his fifth incarnation as a turning point in his life. According to the Tenth Doctor, it was during his fifth incarnation that he truly began to enjoy himself. (TV: Time Crash) (3/3)