In that case the investigation should start asap! How do you feel about Sylvia sending Lancelot to investigate? Since it's your own character, it'll be easier for you to decide what clues to find and so on.

Am I right in thinking he disappears in his own home? I could set up a log for Sylvia and Lancelot to visit and investigate the scene of the crime if you like. Would Childermass still be hanging around?