Under Salt Marsh is set in Morfa Halen, a fictional Welsh town (that translates to ‘salt marsh’). Nestled between mountains and the unforgiving sea, the tight-knit residents are under threat from their very surroundings.

Reilly’s character, Jackie Ellis, enters as a former detective turned teacher. As a brewing storm comes towards Morfa Halen, Ellis discovers the body of one of her pupils, an eight-year-old called Cefin.

The boy, presumed drowned, sets the town alight with theories, digging up a three-year-old cold case that cost Ellis her career – and centres around the disappearance of her niece.

Ellis’ estranged former partner Detective Eric Bull returns to Morfa to help solve the case. The two of them are aware of two things: first, the cases are connected; second, they must solve the mystery before the storm arrives, and destroys all evidence in its wave of destruction.

This is writer, creator and showrunner Claire Oakley’s debut series, following almost five years on from her success with debut feature thriller Make Up.

Oakley says: “Under Salt Marsh is a crime thriller set in a community deeply connected to its environment, and interwoven with the heartache, fears, dreams and secrets of its people.

“At the heart of it all is Jackie, a character who embodies the wildness of the place we're depicting. She's free-spirited, compassionate, and determined, with a steely resolve that makes her truly of the land. We're absolutely thrilled to have Kelly Reilly bringing Jackie to life.”

Under Salt Marsh will air on Sky and NOW, with no release date currently set.