Joanne Froggatt has been cast in a new BBC drama alongside Ben Chaplin and Emilia Fox.
The episode will involve a man whose wife is unaware that he is married to another woman.
Savage's project will feature five 30-minute stand-alone stories written by up and coming screenwriters, with Broadchurch actress Olivia Colman, Alison Steadman from New Tricks and Sightseers' Steve Oram also signed up.
Written by Nick Payne, Colman's episode will follow the life of a vet with a chronically unwell mother.
Sarah Solemani has penned a film she herself will star in, about a bride who discovers her fiancé was once accused of a major crime, while Ashley Walters and Helen Baxendale will feature in other episodes.
"I'm thrilled that Dominic (True Love, Dive) has assembled such a stellar line-up," said Juliette Howell, head of television at Working Title. "It's hugely exciting to see so many of our finest actors bringing these original and distinctive new voices to life."
Filming for The Secrets is currently underway in London, with the series due to air on BBC One later this year.
Teasers for The Secrets episodes
Episode one by Elinor Cook
A man living a secret double life with two wives is exposed. Is monogamy ever a realistic proposition? Starring Joanne Froggatt, Ben Chaplin and Emilia Fox.
Episode two by Nick Payne
A vet expecting her first child is confronted with a moral dilemma - she has all the chemicals to put pets to sleep at her disposable and her chronically-ill mother is wanting to die. Starring Olivia Colman, Alison Steadman and Steve Oram.
Episode three by Ben Ockrent
A girl turns up claiming to be a boy's long-lost sister but there is more to the mystery than first meets the eye. Starring Helen Baxendale, Anthony Welsh and Paige Meade.
Episode four by Nick Payne and Dominic Savage
A police officer's wayward brother has just returned after six months away when an apparent betrayal leads to a confrontation. Starring Ashley Walters.
Episode five by Sarah Solemani
A bride discovers her fiancé was accused of a shocking crime in the past, the night before their wedding day. Starring Sarah Solemani.