Three card murder / J.L. Blackhurst.

The first in a gripping new mystery series introducing Detective Tess Fox and her con-artist sister Sarah Jacobs. DI Tess Fox's first murder scene has two big problems. One, the victim was thrown from the balcony of a flat locked from the inside. Two, Tess knows him. But the biggest problem of all is Tess's half-sister, Sarah. She has links to the deceased and has the skills and criminal background to mastermind a locked-room murder. But she's a con-artist, not a killer. When two more bodies turn up, Tess now has three locked room mysteries to solve and even more reason to be suspicious of Sarah.