When Zoe Heriot was transported back to the Land of Fiction after facing the Cybermen, she created a fictional version of an older Jamie McCrimmon as a friend and a mystery for the Sixth Doctor to solve.
This Jamie, who believed himself to be real, had an identity of Jacobite resistance leader Black Donald, acting against oppressive English forces, lacking memories of his time with the Second Doctor. When he and the Sixth Doctor had resolved the immediate threat, the Doctor invited Jamie to travel with him, Jamie accepting due to his curiosity about the Doctor's claims that they knew each other despite his lack of memory. (AUDIO: City of Spires) He met with Reverend Merodach on his way back to the TARDIS. He became enamoured by his wife, and was disgusted at the sight of them together. (AUDIO: Night's Black Agents) They later apparently landed aboard the RMS Titanic. He went exploring the Ship as he hadn't been on such a ship before. During this time the ship transformed into the Titan which soon hit the iceberg. He was trapped in the sinking ship but was rescued by the Nautilus by Captain Nemo who was hunting a squid that produced the "Black Water". Nemo later drove the Nautilus into a whirlpool the Doctor and Jamie were left in a white void. (AUDIO: The Wreck of the Titan)
The Doctor and Jamie learned that they were in the Land of Fiction, now controlled by Zoe; Jamie's memories of his time with the Doctor were "restored", but he was later revealed to be a fictional construct when a cut revealed that his blood was made of black ink, the lifeblood of the land. Zoe explained that she had created this Jamie to serve as the Doctor's companion and protector after the TARDIS arrived on the outskirts of the Land rather than in Zoe's control room, creating his history as the Black Douglas to give him a suitably heroic backstory in the Doctor's absence.
The fictional Jamie said he was upset about the Doctor never coming back for his companions. He worried that the Doctor never checked on the real Jamie, who might have been hanged by the Redcoats after the Battle of Culloden. At one point, he teamed up to heroically fight alongside Rob Roy MacGregor. Jamie refused rule over the land, which was given to Alice Liddell instead, as he was more of a fighter. Jamie told the Doctor to find the real Jamie if he ever found himself in the Scottish Highlands again. (AUDIO: Legend of the Cybermen)