Tarquin has no particular agenda other than claiming souls, although he did seem to have some age-old grievance with Steve Bradbury, and to that end he even once imbued one of his more prominent servants, Malachi, with great power, so that Malachi could kill Bradbury. However, Malachi failed, and for his inadequacy, Tarquin stripped him of his powers, made him mortal, and left him to die at the hands of Bradbury's subordinates.
Lord Tarquin was one of the primary suspects for the subsequent murder of Bradbury, but it was not he who did that deed. And with Bradbury dead, Tarquin had no further need for dealing with the Sabbat of Maiden Newton for quite some time.
The soul-collecting demon did return to the city, however, to offer the Alliance of Maiden Newton a deal; he would give them the means to destroy their enemy Cornelius once and for
Inside Information: Tarquin began life as a spur-of-the-moment Umbral spirit, to give the PC's some much-needed Gnosis during the Werewolf game, "The Sixth Extinction". But we liked him so much, we kept bringing him back within that Chronicle, and then the following year we just had to find a place for him in the Vampire games as well, even if it was just for a cameo spot. Hence, Tarquin the helpful, camp spirit became Lord Tarquin of the Enslaved Masses, evil demonic overlord.