Finnish spy novel

Here's the cover of Topi Tuisku's aka Topi Vuorinen's spy paperback Kolauta kohtuullisesti ("Bang Slowly" or something to that effect) that was published in 1970, probably as a self-publication, since Iltakirjat (Evening Books), didn't publish anything else. Vuorinen was a business man and I suspect this was his cover-up firm.

The book is nothing memorable. It's a light story about a freelance agent Mikko Sirkkula and his buddy, Max Want, who try to locate secret rocket plans somewhere in Portugal. At one point the spies are dressed as monks, hence the cover illo.