A special release, originally subscriber-only. It was retroactively made available to everyone when it ended up tying heavily into the overall plot of season 4.
It's been twenty years since the future Dalek invasion of Earth was stopped. Susan (still Carole Ann Ford!), the Doctor's granddaughter, has lived a happy life on Earth with her husband David (now dead) and their son Alex. However, traumatised by the Daleks, humanity has become a superstitious and cowardly lot. They're afraid of advanced technology, of strangers, and most of all of aliens. Travel is still nearly impossible and no radio contact has been established with the survivors on the moon colony. In short, it's a Crapsack World.
Since Alex is falling in with the wrong — very xenophobic — crowd, Susan sends out an intergalactic distress call. She's answered by an exploitative alien race called the Guldreasi... and by the Eighth Doctor. Their happy reunion becomes complicated when Susan is held accountable by her alien-phobic society for the Guldreasi's meddling. The aliens do bring back the people who'd been stuck on the moon colony for decades. But, annoyed with the Doctor opposing them, they expose Susan as an alien. The Doctor is forced to defeat them when they turn out to be interstellar slave drivers.
Alex is brought to the TARDIS and has to come to terms with being half-alien. The Doctor wants to take him to Gallifrey and enroll him in Time Lord Academy. Alex instead just storms out. Susan follows him, because no matter how much she loves her grandfather, being a mum is more important now. The Doctor doesn't understand: he's finally figured out the TARDIS controls (... well, sort of), so they can go on tons of interstellar adventures now and he'll still drop her off only a second after they left. Susan still declines — that world just isn't for her anymore.
- Aliens are Bastards: The Daleks certainly were, and even 20 years after humanity defeated them, distrust of anything alien is very common.
- Big "SHUT UP!": From a man at the back of the audience, who's later revealed to be the Eighth Doctor.Let her speak!
- Bluff the Imposter: The Doctor and Marion in the Guldreasi ship.
- Boomerang Bigot: See also Tomato in the Mirror.
- The Bus Came Back: Susan Campbell, the Doctor's Granddaughter from the first episode.
- Call-Back: Several to the events of Dalek Invasion of Earth.
- Cross-Referenced Titles: The story title "An Earthly Child" is a Call-Back to the very first episode of Doctor Who, "An Unearthly Child". Both stories deal with a descendant of the Doctor.
- Fantastic Racism: Earth United and a lot of people are like this to all aliens.
- Half-Human Hybrid: Alex, Time Lord on his mother's side. However he seems more human.
- Older Than They Look: Alex states that the Doctor looks younger than Susan.
- Organic Technology: The Doctor observes the Guldreasi technology to be more organic than technology.
- Paparazzi: Susan is targeted by them.
- Raised by Grandparents: Susan was, at least while she was traveling with the Doctor. We never hear about any other family members apart from her and the Doctor, her grandfather.
- Real-Life Relative: Alex is played by Paul McGann's son.
- Science Is Bad: What many people think of technology due to the Dalek invasion.
- Sequel Episode: To The Dalek Invasion of Earth.
- Special Edition Title: The episode starts out with the original First Doctor theme.
- Tomato in the Mirror: Alex has no idea he's part alien. He's not too accepting of the idea when he finally does learn the truth.
- Wonder Child: The Doctor regards Alex as this, asking Susan how she and David managed to have a half-human, half-Time Lord child. She's rather embarrassed by the question.
- Why Couldn't You Be Different?: The Doctor is rather disappointed to discover that Alex lacks several Time Lord traits, such as telepathy, time sense, and the ability to regenerate.