You could have a flood of memories return to the "sinister" voice, brought about by the true death of Pissy and Jelly. The time frame is a prequel to a story, a setting up of the next book to come. Jelly stumbled upon the removed door and cellar, Pauls being pushed in awoke a long long resting vampire. So long that memories of his past were gone, just instinct to feed. He feeds on Paul, and then Paul brings Angelica to the cellar, the "sinister" voice feeds on her. They all go to sleep, "Sinister" wakes up and see's the others are true dead, but then memories return, and he understands who, and what he is now.

And waking background done, and you do your thing set him on the path of revenge, to get the ancient one who initially turned him, and all the stuff in the middle and the end.