Death was imprisoned below Death’s Sea by a ritual cast by the other Passions due to the threat posed by him keeping one of the Trinity Blades. The Passions involved were Astendaar, Vestrial, Chorolis, Upandal, Floranuus, Thystonius, Garlen, Jaspree, and Mynbruje.
In the first campaign his window on the world, the Bauble of Vestrial had been stolen by Deadwood Martha and he charged the characters to find it. They did so but instead of returning it to Death gave it to Garlen, who intended to us it for another purpose. It appears he had ulterior motives in retrieving this as can be seen in the recent events and the actions of the Master of Shadows