From the Chaosium website:
An 1890s Scenario for Call of Cthulhu and Cthulhu By Gaslight
'Return of the Ripper'takes place in London, beginning in late summer to early autumn of 1893. It involves a new series of killings perpetrated by Jack the Ripper. The Ripper has returned to London to continue his bloody work after a five-year absence. Working in league with the Ripper are other occult horrors with which investigators must deal. At least one of these is far more formidable — and deadly — than the Ripper himself!
The scenario presents a series of clues, encounters, and locations that, explored to their fullest, lead Investigators to the identity — and terrible secrets — of Jack the Ripper. A number of peripheral dangers are encountered along the way that may either be dealt with during the course of the scenario or, in some cases, sidestepped to be handled at a later time — provided Investigators retain life and sanity enough to do so. A number of red herrings are also present, designed to mislead and confuse the investigators. Some of these might lead to entire side adventures of their own; others will simply throw investigators momentarily off the track of their quarry.