The Objet D'Oom was the jar containing Euphemia, the first Scarlet Empress of Hyspero.
It was stolen from the catacombs of the Scarlet Palace by Terrance. Somehow, the Objet became part of the Begins at Home's junkheap.
The Dog Pirates and Anthony Marvelle required the Objet to open up the Ringpull, so the Dog Pirates attacked the Begins at Home, but Terrance took the Objet before the Dog Pirates could get to it, using a transmat to escape. He told Kelly to give the Objet and the Great Big Book Exchange to Simon, and Terrance fled Darlington. Marvelle went to the Great Big Book Exchange, and he stole the Objet from Simon.
When Marvelle took a reluctant Jenny Winterleaf to the Super Hotel Miramar, he entrusted her with the jar, much to her surprise. There she discovered that Euphemia was inside of the jar.
On Valcea, Euphemia would help Jenny remove an explosive device from the inside of Barbra. (PROSE: Enter Wildthyme)