The Sisters of Didacus are a religious order in 80 Days 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 Nova Goa, where Passepartout may be given a Didacian cross. After that they may be met in person in Madras where a nun, Sister Panimalar, engages Passepartout to help them find an automaton with a soul, and to acquire a shard of their control cube for study. There are several such automatons in the game; one between Timbuktu and Marakesh (be sure to make your driver to Tangier go fast, otherwise the automaton's former master will chase you down); one between Munich and Berlin; one from Izmir to Antalya. Additionally, if in possession of the Venetian Glass or a black cube, Passepartout may pass that off as the control shard instead, for which he will received a Silver Chest as a reward.