By Eternally Lost Zeppo

En route to help defend Gallifrey against the Daleks' final assault, the PC Time Lord gets drawn into a pocket dimension, where he finds himself aboard a mysterious structure floating in space.

Meanwhile, three to five other characters from varying times and places are drawn together aboard the structure as well.

If any of them have knowledge of other characters' home worlds and history, they may be perplexed by how those characters' accounts of their world's history differ from what they recall. This is because they may not all necessarily be from the same universe.

Meeting up with each other, the Time Lord and his new companions find that they are not alone aboard this structure. There are creatures infesting it who seem hell-bent on destroying it, and whatever the structure's function is, its systems seem to be failing.

The structure is known as the Watchtower, long forgotten as a myth by the Time Lords, it is a sort of cosmic lynchpin. It exists at the same meta-quantum coordinates across the multiverse, holding all of the different planes of existence together while also acting as a door between them.

However, a force is working against the Watchtower, seizing an opportunity it has been waiting for since time immemorial. But now, with Time Wars raging in the various multiverses, the Time Lords distracted and facing possible annihilation, reality itself is unguarded. The malevolent force which seeks the total destruction of creation is making its move.

Call it what you will, the Darkness, Chaos, has sent its minions to destroy the Watchtower, and with it the last thread holding the multiverse together.

The Watchtower, however, has chosen champions to defend it, and to maintain balance in the Multiverse. This is why the Time Lord and his new friends have been drawn together, here and now. To hold the line against the enemies of creation, no matter the cost.