The 8th of 11 50th anniversary audio adventures from Big Finish Audio, Enemy Aliens is read by India Fisher and features Eight and companion, Charlotte Elspeth Pollard.
Now, unlike the other adventures and the next three, the Eighth Doctor has only been seen in one television movie, about 15 years ago. However, he has had a very active life in Big Finish Audio adventures. This means that, while you don't need to know anything more than, "this is the Doctor and his companion," unlike the other Doctors, you can't just go to DVDs or Netflix or Amazon and catch-up on their adventures. I'll provide a bit of background.
"Charley" Pollard (portrayed by Ms. Fisher from 2001 - 2009) is from 1930s England, born the day the Titanic sank. Young Charlotte was born and raised in wealth -- growing up in a manor house. Calling herself Charley, she rebelled against wealth and privilege. The doctor rescued her from a disaster and she continued to travel with him as a companion. Clever, enthusiastic, curious and headstrong, she's a good fit with the Eighth Doctor. What neither the Doctor or Charley knew, she was fated to die the day he saved her. Her death was one of those "fixed points in time" we Whovians are so familiar with. As the Doctor and Charley traveled in space and time, her existence caused ripples of damaging anti-time. The Time Lords (remember, this is the Classic Era, so the Time Lords still exist) discovered this and the Doctor's former companion and friend, now Madame President of Gallifrey, Romanadveratrelundar reached out to him. Romana pleaded with him to do what is needed -- put Charley back at the moment he found her and let her die. The Doctor refused. Romana, in order to protect the Universe, ordered the Doctor's and Charley's arrest. Dozens of Time Lords led by their special forces were sent to apprehend them; dead or alive. Eventually, the Doctor resolved (cheated) the problem, but this was the point where the Doctor realized he didn't just have differences with his people, but he began to suspect that age, egotism and power have permanently corrupted his people -- even his beloved Romana, and that someday, it would be up to him, and him alone to stop them. Because Charley continued to radiate traces of anti-time, the TARDIS hated her. She was the only companion She didn't inoculate against alien diseases. Charley eventually fell deathly ill and was taken to a hospital world to be healed and recover. In a series of incidents, Charley found herself trapped in the far-far future. She designed a distress beacon and was eventually rescued by The Doctor -- the Sixth Doctor. She traveled briefly with him, but because she couldn't tell him about his future or the paradox or anti-time, she had to constantly lie to him. Her obvious duplicity, coupled with his suspicious nature and the TARDIS' inexplicable hatred of her, led the Six to consider her a threat. Eventually, she left the Doctor and settled back on the planet where she had been healed.
Charley fell deeply in love with the Eighth Doctor, and, to his credit, he actually did say that he loved her; however, she was quickly and ruthlessly "friendzoned" by him.
This story features Charley and The Doctor in 1935, England where they had just finished dealing with an alien threat, when they received (as all the other Doctors in this series have) a message from his future self; specifically, his 11th self. It's a quick story, read well by Ms. Fisher and written by Alan Barnes, a veteran of dozens of Big Finish Audio adventures.