Nathaniel Parker and Sharon Small return as detective duo DI Thomas Lynley and DS Barbara Havers, in four new mysteries. 

Lynley and Havers were first paired up by their boss at Scotland Yard to solve the murder of a farmer in Yorkshire. Despite initial sparks, due to their different upbringings, they cracked the case and a mutual respect blossomed. Now an established team, there's new myseries to be solved, from the missing schoolboy to the playwright killed during rehearsals to the vicar who dies after being poisoned. Among the guest stars in the new series are Martin Jarvis, Jonathan Firth and Cherie Lunghi. 

And when they're not investigating crime, there's plenty happening in the duo's personal lives. Lynley was left devastated when the woman he loved married his best friend. He turns for support to his old friend, Helen (Lesley Vickerage). But, he discovers, there's a fine line between friend and lover. Meanwhile, Havers' father is on his deathbed and she's finding it increasingly difficult to care for her mum, who has Alzheimer's Disease. 

Nathaniel Parker reveals that his main reason for taking the part was the way his character developed. "There's something going on in his life in each story. We've seen him desperately in love with somebody, crying on his best friend's shoulder, and in this series, he gradually falls in love with someone else." Parker admits to loving a good detective story. "I often work out 'whodunit' quite early on. But I love a good thriller. You'll quite often see me at home at the beginning of the episode going: 'Shhh! Shhh! This is the important bit.'" 

Sharon Small relishes playing Havers, someone she describes as not "particularly likeable." But she also enjoys exploring her character's softer side. "You do see her vulnerability at various points and I like playing someone with emotional hang-ups." Sharon, who's also starred in Glasgow Kiss and Sunburn, isn't so keen on Havers' haircut. "It really gets on my nerves. When I want to go out, I can't do anything with it!"