Chessene was the station chatelaine. She was also a subject of Dastari's experimental augmentations, which made her humanoid. After becoming augmented, Chessene displayed vast intelligence and gained the power to read both living and dead minds. Her rough Androgum features softened to human-like in appearance, but she retained her savage Androgum instincts and urges, with both the Second and Sixth Doctors recognising the danger she posed even as Dastari dismissed their concerns, considering her his greatest work.
Chessene made a plan to gain a time machine through experimentation on Time Lords. She made an agreement with a group of Sontarans who promptly arrived on Camera and killed everyone apart from her, Dastari and fellow Androgum Shockeye of the Quawncing Grig. They also failed to kill the Doctor's companion Jamie McCrimmon, who was able to hide on the station until he was rescued by the Sixth Doctor and Peri Brown when they arrived at the station later. Chessene travelled to Spain where they used the captive Second Doctor to search for the ability of time travel which she and Dastari believed was located in a Time Lord's symbiotic nuclei. Chessene killed the Sontarans with coronic acid when they were no further use.
She changed the plan so the Doctor would be turned into an Androgum and tell her where his symbiotic nuclei was located, as well as allowing her to use him as her consort. When the Doctor escaped with Shockeye, Chessene followed him into the town area and eventually found them, but by that point the artificial augmentation had worn off and the Doctor had been rescued by another Time Lord (unknown to Chessene, his sixth incarnation). Although she attempted to force them to finish the Kartz-Reimer module, the future Doctor was able to trick them by creating a link that would only allow the machine to work once.
When Chessene fell to the ground to lick up a fallen sample of Time Lord blood after Shockeye wounded him in a fight, Dastari was forced to recognise the truth of the Doctors' earlier warnings that Chessene's fundamental nature remained unchanged, prompting him to release the captive Second Doctor and Peri. Outraged at his betrayal, Chessene killed Dastari, but was subsequently disarmed by Jamie. She attempted to escape in the module, but it exploded when she tried to dematerialise, killing her. In death she returned to her normal Androgum form. (TV: The Two Doctors)