A lot can happen in a year. Especially if you're a Go Girl.

The popular TV series returns to our screens on Tuesday for a fourth season, with viewers getting reacquainted with their favourite characters one year on from where series three left off. And what a year it's been.

Kevin and Amanda are still married, Amy is back on the Shore with big ambitions, Cody is facing big changes in her lovelife - and Britta has a four-month-old baby girl.

Leighton Cardno, who plays Leo, the deeply sarcastic man with a crush on ditzy Britta, says viewers can expect to be surprised this season - just as the cast were.

"We only get to see stories on a script-by-script basis usually. We were all very delighted and surprised at the directions our characters took," he told Yahoo! New Zealand.

"My character, for instance, is becoming a lot more grounded."

And by grounded, he means Leo is playing a father role to Britta's baby - something even Cardno finds hard to believe.

"[But] even someone as abrasive as Leo's still got a tender side to him," Cardno says. "He's so besotted with Britta, he would do anything to be involved in one way or another in her life."

The story direction meant Cardno had to break that old showbiz adage of never working with animals or children, and he found the babies he and actress Alix Bushnell had to work with "varied".

"Some of the babies were fantastic and would definitely encourage me to run out and buy one, and then there were others that I would thankfully be able to return to the library," he says.

Babies aside, Cardno says he still enjoys playing the acerbic Leo.

"I think I love the fact that I get to say lines that no other character would have got to say. The writers really have given me a wonderful script and vocab," he says of his character's signature cutting remarks.

He's also pleased Leo has got to stick around a bit longer than originally planned.

"I think he was only intended to be around for a very short time, I think three or four episodes, so I was very surprised when the writers responded with wanting to keep him going, which was really cool," Cardno says.

The actor puts the local show's phenomenal success down to its "fantastic" cast, stories that engage viewers - and the fact that 'Go Girls' relates to a wider demographic than its name suggests.

Cardno got a taste of the show's wide appeal during a brief stop in Paeroa.

"I popped into one of the antiques shop, and there were these two old fellas sitting behind the counter ... and one of them saw me and quoted a line from 'Go Girls', a line that my character had said.

"I was quite surprised and was like 'So you guys watch this?' and they said they love it."

So, no doubt the antique shop workers of Paeroa will be joining other 'Go Girls' fans on the couch as series four unfolds - and the question of whether Leo gets his happy ending with Britta is answered.