Synopsis: A long time ago, the Doctor brought a "psycho-sculpture" made by the Telphin to the little English town of Westmouth. This sculpture rested as the town's cenotaph for many long years.
In the present day, that sculpture is calling out to a now-elderly Simon Galway, by projecting dreams of a dying world and his brother's death during a war.
Taking Ace to meet Galway at the cenotaph, the Doctor reveals the psycho-projective properties of the memorial, and that it is actually sending images of the Telphin's defeat by another race, the Chaktra. The Chaktra got a false intelligence report about the Telphin and mistakenly slaughtered the basically peace-loveing race of artists.
In order to preserve something of their species, the Telphin used their artistic abilities to craft a record of their demise.
This "memorial" required a living host until the memory seed matured to the point that it could detach itself from its host. The Doctor, it turned out, had made Galway that host. All the memories he was having of war and the loss of a brother were therefore "false". As the psychic seed and its "memories" depart his mind, Galway is left with a spirit of peace.
Notes: Intriguingly, this story is very similar to an episode of Star Trek: Voyager, also called, "Memorial". This story was pitched to Paramount by James Swallow, a British writer, who has also written novels and audio plays for the Doctor Who universe. Intriguingly, he has also written for the Bernice Summerfield line, a branch of the main Doctor Who universe with its origins firmly in the Seventh Doctor's era of comic stories.
The question thus presents itself: did he lift the idea for his Voyager episode from the pages of Doctor Who magazine? Probably not, but the possibilities are worth mentioning.