Fey Truscott-Sade

Fey Truscott-Sade was an undercover agent for the British government, later companion of the Doctor. Joining with Shayde, both merged into a combined being known as Feyde.

Biography
On an unknown date, she encountered the Doctor (presumably in his eighth incarnation) in an adventure involving psychic weasels in Russell Square. On that occasion the Doctor had given her a Stattenheim Summoner (a device disguised as a tin whistle that could contact the TARDIS). In 1939, Fey called on the Doctor and his companion Izzy to help her investigate the sinister Varney. (DWM: Tooth and Claw).

Unknown to the Doctor, in 1937, time traveling enemies of the Doctor's called the Threshold had kidnapped Fey and put a mind control device in her head. (DWM: Wormwood)

The defeat of Varney proved costly for the Doctor. The Doctor had injected himself with a deadly bacillus and was dying. (DWM: Tooth and Claw) Secretly now under the control of the the Threshold (DWM: Wormwood), Fey piloted the TARDIS back to Gallifrey, where the Doctor's body was cured and his mind placed into the Matrix to heal. (DW: The Final Chapter)

While within the Matrix, an attempt was made on the Doctor's life by a secret Time Lord called the Elysians. The plot was foiled by Shayde, an artificial being created on Gallifrey. The assassination attempt was part of a plot by Overseer Luther. The Doctor managed to thwart Luther by short-circuiting his watchtower (a gigantic TARDIS), but apparently at the cost of his eighth body. As Izzy and Fey watched, the Doctor regenerated into a new incarnation. (DW: The Final Chapter)

However, this was a ruse. The Doctor had realised that Fey was under external control when she had managed to pilot the TARDIS even though the TARDIS manual was in Gallifreyan script, which she wouldn't have understood. Just before the Doctor prepared to sacrifice himself, Shayde offered to take his place and fake a regeneration. This way, would seize the opportunity to bring a newly regenerated and thus weaker Doctor to them. Both disguised with personal chameleon circuits, Shayde would hold their attention while the Doctor sabotaged the Threshold's operations. In Wormwood, a Wild West town on an alien moon run by the Threshold, the Doctor's plans came to fruition. The Threshold removed their implant from Fey, gloating that she had been an unwitting spy for them. Preparing for the final confrontation, Shayde and the Doctor revealed themselves to the Threshold. However, Shayde had to contend with the Pariah, an immensely powerful being who was a prototype version of himself. Shayde was unable to defeat the Pariah on his own, and she crushed his skull. Comforting the dying Shayde, Fey merged with him and together they were able to kill the Pariah and eliminate the Threshold. The shared being, dubbed Feyde by the Doctor, although both of them retained their own consciousness, decided to leave and deal with what had just happened to them. (DWM: Wormwood)

Fey returned to 1939, where she continued to work for the British government. Fey spent two years fighting the Nazis with Shayde, though she felt some frustration because Shayde would not allow her to use their powers to kill Adolf Hitler, as this would have changed history. Over the course of their union, Fey and Shayde began to develop a close love/hate relationship, sharing things about themselves to the other, but often vigerously disputing the use of their power to influence history. Fey resented that Shayde's loyalty to Rassilon was unwavering and that he has seemingly little sense of individuality, yet has proven otherwise in the past. These traits largely imply that she was in love with Shayde, but could not admit this to herself or her partner.(DWM: Me and My Shadow) In 1941, she received a sub-ether summons from the Doctor — Izzy had been kidnapped, and the Doctor needed Shayde's abilities to track her whereabouts on the planet Oblivion. Together, they succeeded in recovering Izzy. After Izzy was sucessfully restored to her own body after having it exchanged with Destrii's, Fey encouraged her (Izzy) to embrace her true sexuality and gave her a passionate kiss. Feyde returned to World War II. (DWM: Oblivion)

Powers
As a merged entity, Fey was able to share Shayde's powers, including the ability to travel through time and space unaided, phase through solid objects and fire self-generated "psychic bullets".

Sexuality
Fey's penchant for dressing in masculine clothing and her relationship with Izzy (herself a lesbian) implied that the former was a lesbian, but her actual orientation was never made explicit, however given certain pieces of dialogue with the Doctor, there is evidence that she could be more accurately described as actually bisexual.