CAST your mind back to the dying moments of the last series of BBC1’s spy drama Spooks. You will recall that MI5 Section D chief Harry Pearce, having just averted a major terrorist atrocity in London, was bundled into the boot of a car by his Russian counterpart, FSB boss Viktor Sarkisian.

The eighth series – which begins on Wednesday – picks up moments after the last left off, but, in typical style, the cast aren’t giving anything away.

‘‘The first episode deals with Harry’s abduction,’’ says Hermione Norris, who plays hard-as-nails agent Ros Myers, ‘‘But after that, the story arc concerns something called Nightingale, which we’re all struggling to understand.

‘‘By episode eight it will all become clear about that and what the threat actually is, but at the moment it’s all a bit of a mystery.’’ While uncertainty hangs in the air after series seven’s cliffhanger, it’s safe to assume Harry will be back for at least the first episode of series eight.

What we do know is former favourite Ruth Evershed is making a return – who knows for how long, but she’s playing a major role in determining Harry’s fate.

‘‘It’s all totally different since my day,’’ says Ruth’s alter ego Nicola Walker. ‘‘My first day was very funny. I walked through the doors onto the grid and thought it would be exactly the same, but of course everything has changed. I kept walking into rooms thinking they were cupboards or toilets, but they’ve become other rooms since I left.

‘‘The set looks a lot more solid and serious now than it used to. I also don’t think anyone tells Ruth that Adam has been blown up since she was last there, either.’’ Details of Ruth’s reappearance are sketchy. The character left the show during the fifth series after allowing herself to be framed for murder to save her boss Harry, the man she loved. In return, he helped her fake her death in order to escape criminal charges.

‘‘No one ever thought Ruth would return because she needed to have a new life and identity,’’ Walker continues.

‘‘She’s had this whole other life, and it’s not the one you might have expected. I thought Ruth might have gone on to a lonely life, in a bad job somewhere where her talents weren’t needed. That’s not the case.

‘‘It’s rare characters can go back to this programme, even if they want to, because there’s a tradition of killing everyone off,’’ she adds. In reality, the actress left to have a baby – her son is now three – but she missed being part of the series.

The last series was enlivened for many a female viewer (and probably a few men too) by the arrival of Lucas North, played by North and South and Robin Hood star Richard Armitage.

Lucas was MI5’s star agent before he was kidnapped by the Russians. He spent eight years as their hostage before being released. ‘‘He was finally adjusting to being released from prison at the end of the last run. This time he’s getting his focus back and becoming the spy he once was,” he says.

‘‘There was a doubt about him last time, whether he was working for the Russians as well as MI5, but now, as far as the writers and producers are concerned, he’s absolutely loyal.

‘HOWEVER, I still think if MI5 doesn’t serve him well enough, he might go where he feels wanted. There has to be a shred of doubt about him. For me, there’s no point playing him otherwise.

‘‘Lucas is a bit of a maverick, and doesn’t always tell people what he’s going to do before he does it. He does something, gets the result then tells everyone when it works out. He serves himself with the thrill of the job.’’ This time round Lucas will have a love interest in the shape of his CIA equal called Sarah Caulfield.

‘‘She challenges him a lot,’’ he says.

‘‘The initial spark is to do with him wanting to match her power, then it does turn into a torrid love affair. It’s dangerous because they’re both players, so it’s more a fractured relationship than anything else. They don’t get a chance to be good lovers, it’s all too tied up in work.’’ ■ Spooks returns to BBC1, Wednesday, 9pm