Kerr's Bernie Gunther series is becoming increasingly hit and miss, and I'm afraid that this book, though quite enjoyable, was overlong and had some incredibly creaky sections. As others have suggested, the romantic interest is little short of risible, there purely to add a little colour and variety to the story: in terms of plot, it has no relevance whatsoever, and is utterly mechanical. One minute Bernie lusts, then is in love, then isn't, then feels bereft ...... I just don't care!
The other really weak section is the solution, which is driven only by the need to keep Bernie alive rather than any function of the plot or character - one minute all is lost then suddenly all is OK. Ta daaaaaa!
I thought 'Prague Fatale' something of a return to form, but I think Kerr's increasing reliance on big stories and big figures from Nazi Germany and WW2, as here with the Katyn Massacre, is a mistake as it weighs down the plot with historical apparatus at the expense of a really interesting thriller. Here, there's enough to keep the flagging fan of the series turning the pages, but another couple like this would turn an interesting and innovative series into pot boiling airport fodder. That would be a real pity: better to kill Bernie off than become so formulaic.