Welcome to Eldey, an island with deadly secrets.

Mona is a carefree artist, staying at The Cloister to work on her illustrations.

Beth is the harried mother of a toddler, on the remote Welsh island for a weekend escape with her family.

Charlotte wanted a romantic getaway with her husband, not a trip with his troubled teenage stepdaughter.

One of them is a serial killer who poisoned three of her friends at her eleventh birthday party.

When one of the hotel guests is found dead, it becomes clear to Mallory Dawson – the night manager of the boutique island hotel and former police detective – that The Birthday Girl is among them.

Three guests who fit the profile, but which of them would risk everything to kill again?