How far do the secrets go back for one mysterious character?

I do love a good thriller and in the mix of many similar styles of strangers in a house/cabin/lodge and who dunnit thrillers this is a refreshing change. The lead character Erma has the heart stopping email of informing her she has a work disciplinary, but little information on why. She suspects foul play by her assistant Jenny - but she has disappeared and may be in trouble herself. Looking forward to discovering these dark secrets!