"I wake up with a big smile on my face at the moment," says spy novelist Mick Herron.
And no, it's not because he's hit the New York Times bestseller list (though surely that's to come) - just that earlier this year he finally quit his job as a sub-editor and now writes full-time.
"I'd commuted from Oxford to London where I worked as a sub-editor for years. I worked very long days, getting on a train a 6.30 am. I was very time poor for a long time," he says down the line from his publishers office in London.
Street Politics
Indeed the genesis of the acclaimed series occurred as Herron was standing on a tube platform in 2005 - the day of London bombings.
"That was one of the reasons I wanted to write books on a broader canvas," he says.
"I realised that day that you don't have to be an expert on geo-politics to write about huge events; you just have to be around when they happen, that offers a way in. I realised that everyone around me was taking part in world politics just by being on the streets of London."
That switch to a wider canvas is now paying off.
Herron's second Slow Horses book Dead Lions (2013) won the CWA Gold Dagger Award, and the next Real Tigers - my favourite so far - was even better. The TV rights to the Slow Horses series have been sold and a pilot script written.
Herron's long been a critic's darling but finally readers too are waking up to his talents.
Jackson Lamb the series' foul-mouthed anti-hero - even has his own Twitter handle @jacksonlambed.
There's an old saying - "happiness writes white" - it doesn't leave marks on the page - whereas grief and despair go much deeper... that's where the humour comes from too...
Spook Street is Herron's 11th novel and the fourth in the Slow Horses series - which has been called "the finest new crime series this millennium".
Last month it won the Ian Fleming Steel Dagger at the CWA awards making it the second CWA Dagger he has won for the Jackson Lamb series, along with four further short listings.
His next - London Rules - is out in February - and is set in the aftermath of Brexit and sees the UK dealing with another string of terror attacks.
No Parody
You finish one Slow Horses book and you devour them all. The prose is immaculate, the humour deft, the characters interesting and relatable.
This is no parody of the form however.
"I don't have a great deal of time for parody," he says.
"I'm attempting to write thrillers that would work if the jokes were taken out."
So, who are these Slow Horses? They're a rag-tag bunch of misfits who've been banished from Regent's House (Herron's fictional stand-in for MI5).
They're there for offences both personal and political their vices are many - addiction, bureaucratic faux pas, failed missions - but it's considered too risky to fire them outright so they're banished to Slough House where they spend their days pushing paper. All long to get back to Regent House and active duty.
"I started with a cast - and I knew they'd be fairly broken individuals. Because I'm writing thrillers and I wanted them to be involved in what was going on they had to be either spies or police officers. If you write about police officers you have to know what you're doing, but if you write about spies you can make it all up - so I went with that."