Free on Amazon UK -
The Black Cabinet: A Golden Age Mystery by Patricia Wentworth
Spoiler:
“I think you’re tempting fate when you say that you will never go back to Danesborough.”
Chloe laughed, suddenly, frankly. Her eyes were black again, and very bright.
“It’s a fate I don’t mind tempting,” she said, and dropped his arm.
Young Chloe, poor but beautiful, is made heiress of her mysterious cousin who has made a tidy fortune in blackmailing. The capital – indiscreet letters which would ruin all sorts of distinguished English people – is kept secret in a safe behind a black cabinet. Cousin Dane whispers the combination to Chloe and straight away dies. But Dane’s big mistake was to have accomplices, and poor Chloe falls into their hands. They will stop at nothing, not even murder, to keep their secrets…
UK
https://www.amazon.co.uk/Black-Cabin...rds=golden+age
US
Not available
Au
https://www.amazon.com.au/Black-Cabi...rds=golden+age
Can
https://www.amazon.ca/Black-Cabinet-...rds=golden+age