In episode 2, DI Ruth Calder makes a huge breakthrough.
In Shetland season 9, DI Calder and DI McIntosh are racing to uncover who murdered local woman Annie Bett and mystery Frenchman Anton Bergen, and why.
And in tonight's episode (Wednesday 13th November), there was a huge breakthrough: Annie and Euan Rossi, her former mathematics professor who recently arrived in Scotland, are spies.
"I was really excited [by that twist]," Alison O'Donnell (Tosh) told RadioTimes.com. "I knew that there was going to be this sort of MI5 element before I’d even read the script, and I thought that's really cool.
"I was in the middle of reading the Richard Osman books at the time, so I was like, 'Oh, I know all about this.' And I think it's really fun territory because you get so much for free with that one. All these people are professionals at skullduggery, so there's so much to be mined there."
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O'Donnell also said that because "the world of the show and the format is so robust now", the writers can take the story in almost any direction.
"Like in season 8, you can take it right down to just this one family [the Bains], this one house, secrets, everything rumbling under the surface, intrigue and lies and cover-ups, and the show can thrive there.
"And then you can go the other way – we've done human trafficking and the far-right extremists in Norway – and take it up to a big, global level, and somehow the show just manages to thrive in both those areas.
"So it's really fun for us to go from one to the other. And with this season, I think they really pushed it off in that direction, having done a more sort of quiet one in season 8."
O'Donnell went on to say that "nothing's quite what it seems" in the remaining episodes.
"This takes us into a dual timeline, things that have happened in the past," she added. "So I'm hoping that people will enjoy the drama of that.
"After all, it is a drama, so hopefully they'll be on board for something a bit more heightened this time."
Shetland season 9 continues on Wednesday 20th November at 9pm on BBC One. Ann Cleeves's Shetland novels are available to buy now.
Check out more of our Drama coverage or visit our TV Guide and Streaming Guide to find out what's on. For more from the biggest stars in TV, listen to The Radio Times Podcast.
Abby Robinson is the Drama Editor for Radio Times, covering TV drama and comedy titles. She previously worked at Digital Spy as a TV writer, and as a content writer at Mumsnet. She possesses a postgraduate diploma and a degree in English Studies.
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