A Secret Killer — Gillian Larkin

Julia Blake runs a cleaning business. She also has the uncanny knack of discovering murdered people.
In this story Julia visits one of her clients, a genealogist called Hugo Barnes. Hugo has uncovered a family secret during the course of his work. He tells Julia that the client won't be happy about the secret he's discovered.
Julia finds Hugo's dead body the next day. She makes her own investigations into Hugo's death and soon discovers that his assistant, Dinah, and his brother, Gilbert have strong motives for killing him.
Julia also finds out who the last client of Hugo's was. Did they have a motive to kill Hugo too?
And who is that man who's been watching Julia's house?
Julia is determined to find out who killed Hugo Barnes.