WARNING: The following contains spoilers for Doctor Who #3 by Jody Houser, Roberta Ingranata, Enrica Eren Angiolini, Shari Chankhamma, and Richard Starkings of Comicraft, on sale now.
At the start of Titan Comics' Doctor Who #1, the Thirteenth Doctor, Graham, Yaz and Ryan returned home to what was supposed to be the present, only to discovery that they had somehow stumbled into an alternate timeline. In this version of reality, the Sea Devils had enslaved humanity a long time ago, and the monsters now ruled over the Earth. The Doctor quickly tried to figure out what had gone so terribly wrong with time and, through her investigation, she learned that this all tied back to one of her previous adventures.
Indeed, the Skithra were ultimately to blame for this change in the timeline. The scorpion-like aliens appeared in Season 12's "Nikola Tesla's Night of Terror," and it's the events of this very episode that the Doctor must revisit to save humanity and restore the timeline in Doctor Who #3.
In "Nikola Tesla's Night of Terror," the Skithra, a race of aliens whose technology was mostly pieced together from what they could steal from others, had failed them and as a result, their ship was stranded near Earth in 1903. In order to fix the ship, they sought out Nikola Tesla, and attempted to kidnap him. Thankfully, the Doctor and her companions intervened and saved the famed inventor from the Skithra.
Now however, the timeline has been altered, and the Doctor has figured out that the point of origin of this change is in 1903 and that it once again involves Tesla and the Skithra. In this version of history, the Doctor wasn't there to stop the aliens from taking Tesla. As a result, the Skithra got what they wanted, and they took things further: they awakened the Sea Devils from their sleep, which allowed the prehistoric creatures to take over the Earth.
Therefore, to undo all of this, the Doctor must revisit the events of "Nikola Tesla's Night of Terror." With her companions, she once again travels to New York City in 1903 but this time, things are different. Indeed, it's not just the Doctor, Graham, Yaz and Ryan who embark on this adventure. No, the group is also joined by three others: a friendly Skithra Queen who wants to help them save humanity, as well as the Tenth Doctor and an alternate version of Rose Tyler.
All seven characters go through some of the same beats that occurred in the episode, from visiting the same locations to interacting with the same people the Doctor previously encountered. But things are also different.With no Doctor, not only was Tesla kidnapped, but so too was his rival, Thomas Edison. Now, both inventors are missing but she has to prevent the Sea Devils from ever being woken up before the Doctor can go save them.
All seven members of the group therefore join forces and travel to the Raven Peninsula in Scotland, where the Skithra plan on unleashing the Sea Devils. Thankfully, the Doctor and her friends are successful: the prehistoric monsters are never woken to begin with, which means they will not rule the Earth years later.
This fixes a part of the timeline, but the group still needs to rescue Tesla and Edison. Only then will the timeline be properly restored. It's more than the Doctor and her companions had to deal with the first time around, but now, they've got some help.