The Unicorn And The Wasp
The TARDIS brings the Doctor and Donna to the 1920s, to an ordinary cocktail party with an extraordinary guest – murder mystery author Agatha Christie. And right on cue, a murder takes place at the party, and the Doctor tries to enlist the famed writer’s help in narrowing down a list of suspects whose alibis have no witness to back them up. Donna searches for clues, and discovers quite a big one – a huge wasp at least as big as a human being. She narrowly avoids its deadly stinger, and at the same time, a jewel thief is at large in the house. But is the killer related to the jewel thief…or the wasp? And after solving a mystery whose perpetrator is not of this Earth, will Agatha Christie ever be the same again?
written by Gareth Roberts
directed by Graeme Harper
music by Murray GoldCast: David Tennant (The Doctor), Catherine Tate (Donna Noble), Fenella Woolgar (Agatha Christie), Felicity Kendal (Lady Eddison), Tom Goodman-Hill (Reverend Golightly), Christopher Benjamin (Colonel Hugh), Felicity Jones (Robina Redmond), Adam Rayner (Roger Curbishley), David Quilter (Greeves), Daniel King (Davenport), Ian Barritt (Professor Peach), Leena Dhingra (Miss Chandrakala), Charlotte Eaton (Mrs. Hart)
Notes: Guest star Christopher Benjamin appeared in two much-loved adventures from classic Doctor Who, the 1970 Jon Pertwee epic Inferno, in which he played well-meaning bureaucrat Sir Keith Gold, and 1977’s Talons Of Weng-Chiang, in which he guest starred as irrepressible showman Henry Gordon Jago – a character who, with Talons sidekick Professor Litefoot, was briefly considered a candidate for an early Doctor Who spinoff which never – if you’ll pardon the pun – materialized. (Jago & Litefoot’s long-overdue spinoff was finally produced in audio form by Big Finish.) Agatha Christie’s amnesiac interlude actually happened, though generally history doesn’t record the whole giant wasp incident in connection with that.
LogBook entry & review by Earl Green
The Doctor and Lucie are aboard a train bound for Sweden in the 1800s; also on the train are priceless artifacts by an artist named Tardelli. This piques the Doctor’s interest: he has followed Tardelli through time and space, removing his artwork, which has a psychically active component that tends to manifest itself as a malign influence wherever it takes root. But two other old acquaintances are aboard the train as well: the Headhunter and Karen, Lucie’s former co-worker who seems to have been liberated from a dark destiny to serve as the Headhunter’s sidekick. They’re also there to pilfer Tardelli’s latest masterpiece, a hefty black diamond, until the Doctor and Lucie intervene in their plans. The two sets of time travelers are in a race to see who can steal the diamond first: the Doctor wants to prevent it from depositing an evil psychic influence on Earth, and the Headhunter’s motive is pure profit… but she hasn’t even told Karen what the real job is, or who they’re really working for. 
Notes: Davros first appeared in 1975’s 
The Doctor and Lucie travel to 1984 to pay another visit to Lucie’s Aunty Pat, and Lucie discovers that Pat’s married to a former folk singer and running a secluded hotel – a marriage that Lucie’s never heard of before. Two other visitors to the hotel also catch the Doctor’s eye; Lucie tries to spy on them, and discovers that they’re Zygons – aliens who can shapeshift to resemble any human that they kidnap and put into their equipment… a fate that Pat’s husband Trevor has suffered, and a fate that now awaits Lucie. The duplicated Lucie tries to throw the Doctor off-course, but even with her interference, he soon discovers that Lucie’s Uncle Trevor is a Zygon warlord who has defected to Earth, taking with him the secrets needed to launch a terrifying new Zygon invasion. Trevor’s fellow Zygons want those secrets, and they’ll do anything, from exposing Trevor’s true identity to killing the human woman he has fallen in love with, to get them.
Trapped in Victorian England without the TARDIS, the Doctor and Nyssa try desperately to track down the TARDIS, ultimately resorting to – out of sheer desperation – convincing guests in a Victorian sitting room to unwittingly participate in a block-transfer computation to allow the Doctor to peer into the time vortex to look for his missing ship. But instead of a peek, the Doctor, Nyssa and two of their unsuspecting acquaintances find themselves transported into prehistoric Earth – but a prehistoric Earth that shouldn’t exist at all. The dinosaurs are nowhere to be found, and giant insects seem to overrun the planet. Even the insects, however, answer to someone else – someone eager to renew his acquaintance with the Doctor and Nyssa. They’re horrified to discover a wizened, demented old man at the heart of this world, a man they once knew as a boy called Adric. Having somehow managed to survive his fiery fall to Earth, Adric has changed history, and he has a score to settle with the Doctor…and he expects to make Nyssa his queen. But is this really Adric? And if so, can his surprisingly vicious taste for revenge be turned into his own redemption before his rule comes to an end?
After a near-miss with the TIme Lords’ time scoop in the vortex, the TARDIS materializes in the cargo hold of a space freighter. The Doctor and Lucie are immediately ambushed the moment they set foot on the ship; Lucie awakens in a prison cell, with no idea who took the Doctor or where he was taken, and is questioned by a large, centipede-like police officer named Rosto, who doesn’t seem inclined to believe a word she says. Straxus appears, asks Lucie about the Doctor’s whereabouts, and then infuriates her by leaving her stranded in Rosto’s custody. A woman appears and attempts to kidnap Lucie, but when her cover story slips, Rosto comes to the rescue. Lucie’s would-be kidnapper vanishes into thin air, but not before Rosto identifies her as the leader of the raiding party that took the Doctor. Rosto and Lucie follow the clues and discover that the woman was a member of an obscure mystic sect called the Sisterhood of Karn. Rosto and Lucie travel to Karn, hoping that they’ll find the Doctor there, unaware that a much larger crisis looms, endangering the whole universe.
The Doctor and Lucie are reunited by the Sisterhood of Karn, but the Sisters plan to summarily execute them both, eliminating the Doctor as a potential subject for gene-splicing experiments to revive Morbius. However, the Sisters have miscalculated: the Doctor isn’t the only Time Lord available to become an unwitting DNA donor to revive Morbius. Forced down on Karn, Straxus becomes the donor and Rosto is enslaved. The new reign of Morbius begins. The Doctor and Lucie are whisked away to Gallifrey, already under siege from Morbius’ forces. Unsurprisingly, the Time Lords respond to the crisis by going into hiding, while the Doctor and Lucie use the TARDIS to go to Karn. With the Time Lords cowering, the Doctor is ready to take Lucie’s advice: he plans to cross his own timeline and prevent Morbius’ rebirth from taking place. But with Gallifrey’s Eye of Harmony faltering under attack from Morbius, the Doctor’s TARDIS misses the intended temporal destination and arrives ten years into Morbius’ new reign of terror.