Anthony Gilbert 
The Visitor [EPUB ebook] 

A blackmailer – murdered. And the suspect in fear for her life… Classic crime from one of the greats of the Detection Club Margaret Ross knew she had to pay off the blackmailer, Samson, or else her beloved son would go to jail for forgery. The next night she rang the bell at Samson’s sinister house on Margate Street. There was no answer. Slowly she entered the house and went up the stairs. Samson was waiting at his desk – murdered. She found the incriminating letters and the cheque and escaped with them. But she had been seen. The dangers gather like wasps around Margaret and it takes all of Detective Arthur Crook’s genius to get to her in time. 'Amusing and zestful, with an unexpected and exciting climax’ Daily Telegraph