When a family meets for a celebaration in a cottage on Bardsey Island, for some it is a rare opportunity to see relatives, while it is a task to be unwillingly suffered for others. A stranger arrives at the cottage, and many secrets are revealed. A mystery about a family in isolation on an island with a murderer amongst them.

Pan fo teulu yn cwrdd am ddathliad arbennig mewn bwthyn ar ynys hudolus Enlli, mae'n gyfle prin i ddod ynghyd fel teulu i rai, ond i eraill mae'n orchwyl y mae'n rhaid ei diodde'n anfoddog. Yng nghanol y storm daw dieithryn i'r drws, a daw sawl cyfrinach i'r wyneb yn ystod eu cyfnod clawstroffobig ar yr ynys.