During the Liberation of Rome the Borgia threw a jubilee, and the Duchess of Urbino decided to attend it, even though the relation between both families were heavily damaged by Cesare's attempt to conquer all of Italy.
The Assassins knew that the Duchess was working against the Templars and decided she was an ally they could not lose, and they came up with a plan to prevent her from attending the jubilee. They disguised themselves as workers and urged Elisabetta to come with them, but the Duchess, only seeing their worker-outfits, declared she would stay out in the streets. Her objections caused several guards to arrive on the scene, after which Francesco Vecellio threw a smoke bomb to hide the events from them.
The smoke bomb was also a sign for Tessa Varzi to prick the Duchess with a poisoned blade, causing her to faint and allowing the Assassins to get her to safety. They placed her in a carriage bound for Mantua, knowing she and her family would continue their struggle against the Borgia.