IT’S BEEN the best TV cat and mouse act since Tom and Jerry.

Now, River City’s DI Donald and gangster Lenny Murdoch are set to surprise viewers by ceasing the flying fur – for a while at least.

What we already know is that DI Donald and Amber, Lenny’s daughter, are having ‘a thing’.

But actor Robin Laing, who plays the dogged detective in the BBC drama, explains how this is why the Shieldinch sworn enemies come to team up.

“DI Donald and Lenny are in the invidious position of having to rely upon each other,” he says, smiling.

“We learn that Belinda, Amber’s ‘prison wife’ has secreted Amber away somewhere.

“So now Lenny and Donald have to not only come to a truce but suddenly build a trust to make sure they can get Amber back.”

Trust between the two will be hard to gain. And of course the relationship with DI Donald and Amber has never been solid; neither is sure of the other’s motives.

But can we assume normal hatred between Donald and Murdoch will be resumed as soon as possible?

“The fall out will be fascinating,” says Robin, smiling. “Watch this space.”

Robin, who studied drama at Fife College, has created a pivotal, and entirely convincing character in DI Donald.

Initially drafted in for just three weeks, he came up with a great character note which made sure viewers loved watching his detective.

“I had been watching (the HBO series, screened on the BBC) series Boardwalk Empire at the time and it featured a policeman, played by Steve Buscemi, a guy who goes home at night and whips his own back.

“I said to the River City producer that DI Donald is that sort of character, someone obsessed with his work to the point of madness.”

Robin adds; “DI Donald is so much about the work he doesn’t even need a first name. He is just The Law.

“And in fact it was 18 months before we learned he has a first name. (Craig).”

Robin loves playing his character.

“He has moved slightly either side of the line of moral ambiguity. In his determination to put Lenny away he makes us ask the philosophical question about whether you can justify bending the law to uphold the law.

“When you are isolated in your own bubble and it becomes them and us, you can see how the normal rationale goes out the window.

“And you are in an emotionally fraught situation.”

DI Donald’s rationale certainly does go out the window at times.

And it’s fascinating for viewers to see how far he will go with his obsession to beat Lenny.

But Robin, who has starred in cult theatre plays such as The Slab Boys and Trainspotting (he played Renton) is currently focused on more than playing a convincing character.

He reveals he’s also stepping across to the other side of the camera, directing episodes of River City.

How do his fellow actors around feel about him pushing them around?”

“They have all been very gracious and willing me on,” he says, laughing.

To your face, at least Robin.

“Yes,” he says, laughing. “Who knows what they’re saying in the Green Room. But I love it, I’m now working 12 hour days.”

It is just like a real job?”

“It is,” he says, grinning, “although we still work in blocks so it’s not quite real.”

Outside of River City Robin has stayed in nice work.

“Last summer I worked in Devon on the BBC drama The Coroner, a couple of years ago I was in the Irvine Welsh film Filth.

“And I was in a great David Leddy play at the Tron Theatre at the beginning of the year.”

And home life is never quiet.

“I have two boys,” he says, the pride in his voice audible. “So there is always someone to be taken to piano lessons, or football training.”

Robin was surprised however to learn he has a Wikipedia entry - in Spanish.

“It’s most likely as a result of the Band of Brothers fans,” he says of his stint in the BBC series. “They are very loyal and dedicated.

“But it’s great because my parents live in Spain and speak Spanish. They’ll be delighted to read about me.”

He adds, grinning; “I just hope it says something nice about me.”

Robin is still in touch with the Band of Brothers actors and travels to Normandy with The World War 2 Foundation, the non-profit group which educates young people about those who made incredible sacrifices during war.

“I meet up with the cast and the veterans and we do Q&As and signings, and help makes films about the war which are distributed to schools.

“It’s an emotional time, going over there and meeting up with the incredible men and women who took part in the war.”

He adds, “It’s all incomparable to playing the role of a soldier on television.”

Meantime, what’s on the cards for DI Donald beyond the love affair with Lenny?

“The producers try and give us an overview at the start of the three month filming block, but that can all change.

“So we usually get quite a surprise.”

Robin grins as he adds; “The first thing you do is pick up a script and see how many scenes you have.”

Surely you pick up the script and look to make sure that DI Donald isn’t lying on a pavement with chalk marks all around him?

“Yes,” he says laughing.

“That’s the joy of the business. You are only ever one script away from switching to an interest-only mortgage.”

• River City, BBC 1 Scotland, Tuesday at 8pm.