Author Tom Scott has a line he is particularly proud of in his screenplay for the 2009 New Zealand film Separation City.

It's delivered by main character Simon, a parliamentary press secretary who, after years in a slowly chilling marriage, has became infatuated with Katrien – a beautiful cellist who is also his wife's friend.

Fast forward to the inevitable fallout and a scene where a forlorn but reflective Simon is shopping for a potato peeler and other necessities for his new single guy flat.

How is he coping?

"I'd reverted to the time-honoured practice of men down the centuries," he says. "I was bottling up my feelings and growing a tumour."

It's a beautifully observed line in a well-observed dark comedy which explores the complexities of love with such humour and insight that it elevates the film above the often humdrum portrayal of onscreen relationships.

Part of this could be a result of Scott, a cartoonist, writer and director, basing some characters and situations in the film on people he knew and things he'd personally experienced.

The men's group that Simon (Joel Edgerton) reluctantly agrees to go to is based on meetings that Scott and a friend attended "back when we were silly young things and we thought that men were the enemy and we all needed to improve".

His friend was very funny, open and honest, says Scott, especially about his relationship, sharing stories including that his wife said they could have sex as long as she was allowed to keep reading. These stories were so amusing to Scott that they inspired the idea for Separation City.

"I thought gosh, there's a story here about men trying to be better and I just thought, there's a dark comedy."

The plot is based around the central relationship between Simon and Pam (Danielle Cormack) and their wider group of Wellington friends. It's a darkly comedic story but not without sweetness.

One of Scott's other favourite lines comes near the end of the film where Simon muses: "Love is a moving sea. There are times when the tide goes out leaving you stranded; then you have to be strong and patient and wait for the moon and stars to work their magic again."

Separation City has a superb cast of actors who give fine performances and Scott speaks fondly of all of them. Cormack certainly shines in her role as Pam.

"She was one of the first actresses to read for the part and I said, `We don't need to audition anyone else' and they said `We have too' and I said `We don't, we've got her, she's nailed it, absolutely nailed it'. She's a tremendous actress."

And, just in case you're wondering, there is another standout moment in the film based on fact – the scene where (slight spoiler alert) a drunken Simon throws a chair out of a Berlin hotel window actually happened in Scott's hotel room during a National Party conference in Christchurch.

A political cartoonist for The Listener at the time, he had just been sued for libel by Robert Muldoon and the then prime minister had made Scott stand up at the conference to the cheers/jeers of the National party audience. When Scott returned to his hotel that night, he found around 30 young Nats partying in his room.

"I was like a one-man Rolling Stones band and I was an innocent in the middle of all this chaos", he says. "And one of my friends threw an arm chair out of the 12th floor of the Noah's hotel. It exploded when it hit the street. It's a wonder no-one got hurt. All these things that are horrifying at the time, you can laugh about later."

Separation City screens tonight on TVOne at 8.35pm.

- © Fairfax NZ News