Thomas Brewster, Dickensian orphan, tells the story of his life. At the age of four, he watched as his mother's corpse was displayed at her funeral — his earliest memory of the woman. She'd drowned herself out of shame, having given birth to a bastard son. None of her relatives were willing to take care of Thomas, and so he ended up in the workhouse, where he spent the rest of his childhood. He started hearing his mother's voice soon after, singing to him from the afterlife. And Thomas never heard the Fifth Doctor and Nyssa visiting the workhouse to ask about him and the voice that plagued him.
At the age of fourteen, Thomas was bought from the workhouse by a scavenger named Creek, who beat his boys and had them dredging up goods from the muddy river. Still beset by the sound of his mother's voice, Thomas found it hard to get used to his new life. But soon, he and his new friend — a boy named Pickens — dug up a old police box from the river, and from the looks of it, the box had been down there for decades. Creek began locking up Thomas inside the shop, having him work long hours for months, and Thomas couldn't do anything but sit and listen when the Doctor and Nyssa came around to ask for him. Creek, suspecting that the boy might be hiding something from him, tried to drown Thomas in the river... but slipped. Thomas half-heartedly offered Creek his own whipping stick to grab onto, but ended up watching as Creek drowned. He and Pickens grabbed the shop's boat and left through the thick fog, and Thomas tried his hardest to ignore the guilt inside him, the vision of his mother's bloated, rotting face in front of his eyes — and the boat in the distance carring the Doctor, Nyssa and someone else, calling out to him.
The Doctor and Nyssa investigate a power cut in the TARDIS. In the pitch black engine rooms, they hear a woman's voice singing to them. Just as the Doctor realises there's a rip in time, Nyssa is thrown out of the TARDIS entirely and ends up in London, 1867. A kind young man named Robert soon comes to pick her up and takes her to his master: the Doctor, who's been living as a scientist in London for a year. He's grown a beard, bought a house in Baker Street and taken on an apprentice, in order to ingratiate himself to the Royal Society. After being reunited with Nyssa, he explains that the TARDIS stranded him in 1866. He's been "borrowing" scientific equipment of the age in order to repair his TARDIS and locate the origin of the time rips. However, London's scientists have been plagued by thieves, who steal very specific equipment. Said thieves — Thomas and Pickens — soon appear to steal the Doctor's technology as well as Nyssa.
The Doctor and Robert track down the thieves, who turn out to be building a Steampunk time machine. Thomas (now only going by "Brewster") continuously sees his mother's rotting face and obeys her instructions to build the device. She claims it can bring her back from the dead. Once activated, the machine of course does nothing of the sort, but instead brings about a race of evil gas creatures. They promptly kill Pickens and head off to conquer the rest of Earth.
The Doctor and Nyssa find out what the creatures are: an evil race from a highly improbable future, who want to create themselves in 2008 by making their improbability in 1867 into a probability, then into a reality. They've been impersonating Brewster's mother to him, and trick him into believing that the Doctor's explanation is a lie. Robert, meanwhile, is gutted to discover that the Doctor has been lying to him for a year, and announces that he wishes to end their friendship, although preferably on amicable terms. Once the gas creatures start invading Baker Street through the chimney, however, Robert instead makes a grand Heroic Sacrifice to hold them off. Brewster steals Nyssa's TARDIS key, lets his "mother" guide his hands on the console and vworps off.
Nyssa remembers Thomas telling her about Creek's shop, and decides that investigating it is a better plan than sitting around panicking. Inside the abandoned shop, they find the TARDIS — who spent over 30 years in the river — and check her logs. The Doctor takes her and Nyssa back to the moment where Brewster took off to: 2008, the future in which the creatures have destroyed the planet. He lands the TARDIS inside her own console room, picks up Brewster, sets Brewster's version of the TARDIS to vworp into the past to the bottom of the river (in order to seal off one end of the time corridor), and has his own version of the TARDIS disappear just one moment earlier (in order to seal off the other end).
With the creatures' time portal now closed, Brewster becomes a living paradox and falls very ill, still also not wanting to believe that his visions of his mother were not really her. Nyssa and the Doctor try to pinpoint the moment the gas first started influencing Brewster, in order to erase the remaining parts of the paradox. They watch him at the funeral; ask for him at the workhouse; try and find him at the shop. Meanwhile, the voice is now telling Brewster that he's a killer, that caused the deaths of Creek, and Pickens, and Robert, and that he should kill again. Brewster finally realises that the hallucinations are not his mother, since she would never ask him to kill. He reveals that he first properly saw his mother during his escape from Creek's shop, and so the Doctor and Nyssa take him to the river, where they spot Brewster's boat from afar. Despite the Doctor's warnings about preserving the web of time, Brewster calls out to his past self, warning him that the vision is not his mother at all. Since this causes past Brewster to dismiss his first visual hallucination and all subsequent ones, the paradox is neatly resolved and Brewster is free from his malady.
In the end, Brewster makes peace with his memories, and the Doctor and Nyssa plan to find a good home for him. Brewster instead decides to take matters into his own hands and steals the TARDIS again.
Tropes:
- Action Film, Quiet Drama Scene: Robert telling the Doctor he wants to end their friendship over the Doctor's year-long deceit, and Nyssa and Brewster discussing what it feels like to be orphaned.
- Author Appeal: Jonathan Morris loves a good Timey-Wimey Ball.
- Bad Future: The phantoms are from a future where they exist, and mankind doesn't.
- Blackout Basement: The TARDIS has a total power outage, forcing the Doctor and Nyssa to go through the wine cellar that the Doctor didn't know he had.
- Call-Back: The Doctor says the future of Earth is "Ash and Clinker"
- Energy Beings: Gas beings, akin to those of "The Unquiet Dead".
- Here We Go Again!: The episode ends with Thomas stealing the TARDIS again.
- Homoerotic Subtext: There's a few hints to the effect that Pickens loves Thomas.
- Ironic Echo: The Doctor at first doesn't take Nyssa seriously a few times and she asks if he's mocking her. When they get separated and the Doctor had to take The Slow Path and grew a literal beard, he asks if she's mocking him.
- Ironic Nursery Tune: "Oranges and Lemons" once again makes an appearance in Big Finish — it's starting to become a somewhat macabre Running Gag.
- My God, What Have I Done?: Finishing the machine makes Thomas exclaim this.
- Shout-Out:
- The Doctor announces sarcastically that he'll be doing some deducing — it might even be a three-cups-of-tea problem.
- The Doctor strongly references Robert A. Heinlein's By His Bootstraps.
- Narrator: Thomas narrates this story.
- Never the Selves Shall Meet: The Doctor mentions Thomas should never touch his previous self, in a reference to the show's Blinovitch effect.
- Portal to the Past: The machine Thomas' mother has him make is one of these (but on the receiving end of the "Past" in Portal to the Past)
- Recurring Riff: There's a few background tunes that come back, especially the four chord violin.
- The Slow Path: Nyssa gets removed from the TARDIS and ends up later in the time period than the Doctor. The Doctor in the meantime has grown a literal beard, named himself Dr. Walters, and taken on an apprentice.
- Temporal Paradox: Two. The existence of the creatures, and Brewster undoing the timeline by warning himself.
