This is the infamous paperback I paid 20 kr for in Stockholm. Apparently her first novel, which I didn't realise at the time - I just noticed that I didn't recognise the title so I bought it.
In the early days Alleyn has a journalist sidekick named Nigel Bathgate, who makes his appearance here. Bathgate gets an invitation to a week-end house party through an older cousin. The weekend is going to be spent playing a variation on a murder game - and you guessed it, there's a real murder.
While this has that lovely Marsh touch as far as language goes, and even some of the wry humour, it's still a bit rough. Alleyn is much too quick to feel certain that Bathgate's alibi is solid (based on three cigarette butts in an ashtray - I mean really), and even odder still he takes him completely into his confidence and allows him to join in a spy hunt. That's a bit absurd. But I still enjoyed it well enough.