Tegan Jovanka was an Australian air stewardess, and the main companion of the Fifth Doctor, although she initially met the Fourth Doctor on his final adventure. She quickly became embroiled in the events surrounding the Doctor's regeneration and found herself a unwilling passenger of the Fifth Doctor with Adric, and Nyssa, as the Doctor failed to successfully return her to her proper time and place. Some time after being returned to Heathrow, she reunited with the Doctor in Amsterdam, and rejoined him and Nyssa.
During her adventures with them, she was troubled by her possession by the Mara. Some time later, they were joined by Turlough, who she was somewhat suspicious of, and later Kamelion. Theu would adventure together for a time, until the stress of her adventures bacame too much.
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While en route to Heathrow Airport with Autie Vanessa for a job interview as an air stewardess, Vanessa's car suffered a flat tire. Seeing what she thought was a police box, Tegan tried to call for help to fix her aunt's flat tyre. Having instead entered the Doctor's TARDIS, she got lost within it's vast dephs, and was an unwitting passenger when the Fourth Doctor and Adric headed to the planet Logopolis.
Finally meeting the Doctor and Adric, they could not immediately return her, as they soom found themselves dealing with the threat of the Master using Logopolis's science for his own ends. During this time, she also met Nyssa, who had been taken to Logopolis as well. Tegan was heartbroken to learn that the Master had killed her Aunt for his own sick pleasure. When the Master's interference led to the universe beginning to unravel rom entropy, they returned to Earth, and headed to the Pharos Project, to open a CVE and thus save the universe. After the Master was defeated, she witnessed the Doctor's fall from the Project's radio telescope and his regeneration.
Left to look after the newly regenerated Fifth Doctor, Tegan and Nyssa were critical to stabilising the Doctor's difficult regeneration. When the Master sent the TARDIS to the Big Bang, Tegan was able to pilot her away, unaware she was being further manipulated by the Master. After his trap was thwarted, and with the new Doctor recovered, Tegan joined him for the time being, until he could return her to Heathrow. Throughout her initial batch of adventures, she wore her uniform, as if to remind everyone of her goal.
In Kinda, after arriving on the planet Deva Loka, Tegan fell asleep under the wind chimes, and found her consciousness in a black void. Seeing an elderly couple playing chess, who did not acknowledge her existence, Tegan encountered Dukka, a manifestation of the Mara, who confronted her with paradoxes of existence; splitting her into two beings and orders them to argue which one is real. After tormenting her further, Tegan she agreed to let the Mara take control. After the Mara tokk another host, Tegan helped to stop it with a circle of mirrors, but was left disturbed by the experience.