A majority of Martin Freeman’s small screen detective work as Dr. John Watson has been spent endlessly marveling at the other-worldly deduction skills of Sherlock Holmes, the world’s most recognizable consulting detective.

Now the Sherlock star will soon shed the need to always wonder “What would Sherlock do?” for his new ITV series, A Confession.

With Freeman now assuming the role of lead detective and finally out from under the shadows of Sherlock’s deerstalker hat, the six-part series tells the true story of Steve Fulcher, a detective superintendent who deliberately breached police procedure to catch a killer. The decision cost him his career and reputation.

Set in Swindon, Wiltshire, A Confession will dramatize the real-life case of 22-year-old Sian O’Callaghan, who disappeared in 2011. As senior investigating officer, Fulcher comes into contact with Sian’s mother Elaine — played by Downton Abbey’s Siobhan Finneran (Sarah O’Brien) — and becomes convinced the missing girl is still alive.

Written by Jeff Pope (Philomena), the series centers around Fulcher’s internal struggle of having to race against time to save lives while, ultimately, denying a suspect his rights.

“I found this is a fascinating story to tell on a number of levels,” he said in an ITV release. “On one hand it is a brilliant piece of detective work, but in order to find both girls, Fulcher felt he had to deny Halliwell his rights as a suspect.

Pope said it brings into question how we want our police to behave when someone goes missing. “Should Fulcher have been praised as a courageous officer fighting for the life of a girl, or lose his career for riding roughshod over the law?”

Filmed in Wiltshire and the Home Counties, A Confession will also star Imelda Staunton — who has her own real-life Downton Abbey connection, having been married to Jim Carter (Mr. Carson) since 1983 — and Joe Absolom (Doc Martin).