"It's got to have a limit."
Ahead of Shetland's season 9 debut this week, Alison O'Donnell has spoken to RadioTimes.com about when she will decide to walk away from the BBC crime drama.
"Always in the back of my head is [that] I would hate to have come this far and then to just slightly overstay my welcome," said the Tosh actor.
"So I would always have one eye on, OK, is this the moment? Because you feel like you sort of are traversing up the way, like a roller coaster, and we got a little extra boost with season 8 and the sort of refresh.
"I just would love to find the moment where we reach the top and then quit. I wouldn't want to start going down."
O'Donnell went on to say that while "everybody is happy to sort of suspend their disbelief for the sake of the show" and keep on going, "so much time in that small place, it's got to have a limit".
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"But even if I got to the point where I thought I should step back, it may very well carry on without me," she added.
"I couldn't imagine the show without [Douglas Henshall as Jimmy] Perez. To me, that was just unimaginable. And then we did it. So it's not impossible."
In the latest batch of episodes, a double missing persons case "blurs the line between the personal and the professional" for Tosh, while DI Ruth Calder (Ashley Jensen) "delves deeper into another case involving a deadly argument between two brothers".
"Tosh has an unshakeable integrity," O'Donnell told the BBC. "She's always going to do the right thing by the investigation, which may not always sit well with her friends.
"Everyone is feeling compromised, stressed and mistrustful, and these friendships are going to be tested... every stone must be unturned and a lot of secrets are going to come out."
Several familiar faces return alongside the two lead detectives, plus multiple new guest stars, including Ian Hart, who you might recognise from Mr Bates vs The Post Office and The Responder.
Shetland seasons 1-8 are available to stream on BBC iPlayer. 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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