No, it's bugged.
Did you talk to Tarquin after arriving on the mainland?
He just vanished for me, so I couldn't trigger the quest :/
Just after arriving at Stonegarden, he appeared me for me on Lady Vengeance, with no quest either.
I hope Larian Studios fixes this quest fast, because Tarquin's quest seems to have major consequences on the story line.
I hate to miss out on sth, thats why this game is on hold for me.
