they were in sherlock holmes' room and Dr. watson said that he should clean his room. right after he said that sherlock pulls out one of his mystery cases and tells him about the musgrave ritual.
in the mystery that sherlock holmes tells his college friend he is at the part where he catches brunton the butler looking through the musgrave documents. so when this happens he told bunton that he had one week to leave the hearlstone mansion
after a couple days of the whole event happening with the ritual he then had disappeared. and when his ex girlfriend head about this she also went crazy.
after sherlock holmes finds out that brunton and rachel disappear he goes to investigate. in the investigation he has to do the musgrave ritual in order to find out where brunton and rachel went.