For those wondering what the story was behind Matthew Lewis' 19th century English Policeman outfit on Twitter Monday, it has been revealed that he will costar in the fourth season of hit series Ripper Street. The programme will air exclusively in the UK and US on Amazon Prime online.

Sometimes I like to dress like a 19th Century policeman and insist somebody takes pictures of me next to a horse. pic.twitter.com/xdStaC2cMc

— Matthew Lewis (@Mattdavelewis) August 10, 2015

#RipperStreet adds David Threlfall and @Mattdavelewis to its cast as series 4 filming begins: http://t.co/uUAda4kTrS pic.twitter.com/1abkHPjfTB

— Digital Spy TV (@digitalspytv) August 11, 2015

More on the show now costarring the Harry Potter alum can be read below. For those interested in catching up on previous seasons of Ripper Street, watch it here.

Picking up in 1894, four years after the culmination of season two, the new season reveals a vivid and sensual descent into the lives of the men and women who must live on the violent streets of Whitechapel in late Victorian London.

Matthew Macfadyen returns as Detective Inspector Reid, Jerome Flynn as the newly promoted Detective Inspector Bennet Drake, and Adam Rothenberg as Captain Homer Jackson. MyAnna Buring also returns as Long Susan in the eight-part season.

Four years have passed since Reid bayed for Drake to end the life of Jedediah Shine. Four years that have seen the crime-fighting axis of Reid, Drake and Jackson split and isolated from one another. Drake has left London for Manchester to become the policeman – and man – he felt he could no longer be in Whitechapel. He is an Inspector himself now. Jackson has reverted to the man Reid plucked out of the Tenter Street brothel, a two-penny, sawbones, clap-doctor. And Reid has succumbed to his own shame and isolation, policing Whitechapel with a level of forensic detail and dedication that leads Chief Inspector Fred Abberline to fear for his old friend’s mental well-being.

Meanwhile, Long Susan has made good on her threats to both Captain Jackson and the dying Silas Dugan – she has separated from her husband, taken command of Duggan’s criminal empire and turned it into a legitimate property empire of huge philanthropic ambition. But such aspirations are costly, as her loyal but scheming solicitor Ronald Capshaw knows only too well.

All these resentments, fears and ambitions are soon forgotten, however, when two trains collide on the newly constructed bridge above Leman Street. It is a catastrophe which falls into Reid’s world and demands explanation. His pursuit reunites him with Drake and Jackson and sets him on his own collision course with his past and with the secret crimes of Long Susan and Ronald Capshaw.

The third season of Ripper Street was filmed in Manchester, Loughborough and Dublin and is produced by Tiger Aspect Productions and Lookout Point. It is co-produced by BBC AMERICA and Amazon Prime Instant Video, and distributed by BBC Worldwide.