The Sisters of Didacus are a group of characters in 80 Days. They are a religious order that believe automatons have souls. This brings them into direct contradiction with the Pope (who believes automatons are abominations) and the Artificers Guild (who believe automatons are tools to be used to benefit humans).
The Sisters are first met in Madras where they engage Passepartout to help them find an automaton with a soul, and then a shard of their control cube back to them for study. There are several such automatons in the game; one between Timbuktu and Marakesh; one between Munich to Berlin; one from Izmir to Antalya. Additionally, if in possession of the Venetian Glass, Passepartout may pass that off as the control shard instead, for which he will received a Silver Chest as a reward.