Doctor Who showrunner Russell T. Davies has hinted at how David Tennant and Catherine Tate are returning in the show's 60th anniversary celebrations. Doctor Who has traditionally celebrated its anniversary with multi-Doctor stories; the first of these was 1973's "The Three Doctors," and the most recent was "The Day of the Doctor," which even released in cinemas. But returning showrunner Russell T. Davies seems to be taking a different approach for the 60th anniversary.
David Tennant and Catherine Tate - fan-favorites who played the Tenth Doctor and his companion Donna Noble - are indeed returning. But rather than appear in a multi-Doctor story, they seem to be starring in their own adventure, one in which they go head-to-head with Neil Patrick Harris as a mysterious villain. The BBC has yet to officially confirm Harris' role in the Doctor Who 60th anniversary, but set photos have shown him in an old-fashioned toy shop, with awards celebrating him as "Toymaker of the Year" - heavy hints Harris is playing a classic villain called the Toymaker, who caused problems for William Hartnell's First Doctor.
The precise circumstances of Tennant's and Tate's return are a mystery at present, and will no doubt remain so for as long as possible. Still, in an interview with Doctor Who Magazine published in #579, Davies addressed all the popular theories.
"How the hell can the Doctor and Donna be reunited! You're sci-fi fans, you know the score, there are all sorts of possibilities ahead. Virgin Publishing once had a fine range of novels called The Missing Adventures - is that what this is? A mysteriously forgotten excursion for the TARDIS in between Planet of the Ood and The Sontaran Stratagem? Or maybe it's a multiverse thing, they're all the rage these days. Maybe this is a Doctor and Donna from Universe 557, all set to collide with our own. Then again, maybe, just maybe, this return is so impossible that it's actually an intricate illusion created by an old enemy of the Doctor's. Or maybe an old enemy of Donna's."
The sense of mystery is undoubtedly making Doctor Who quite exciting for the fan community, and Davies' comment shows just how familiar he is with the conversations. He essentially sums up all the top theories, and it's interesting to note he focuses on the last possibility that's only recently been suggested in light of Harris' casting. The Toymaker is indeed just such a classic foe who could project an illusionary Doctor; in fact, in the 1966 story "The Celestial Toymaker," he made the First Doctor temporarily invisible, and the producer at the time considered using this as an opportunity to recast the role of the Doctor (he was overruled, and some months later writers came up with the much better idea of regeneration).
Davies' final remark is curious, though, in that it suggests the Toymaker's illusions are being performed on Donna Noble rather than on the Doctor. Donna's memories were erased by the Doctor after she downloaded his mind into her own consciousness; the experience would have been too much for her human mind to handle, and the Doctor was forced to make her forget all about her travels with him. The Toymaker is a powerful enough entity to reverse that, and he'd surely enjoy the idea of playing with someone who had meant so much to the Doctor. That really is an exciting idea for the Doctor Who 60th anniversary.