I've been reading a lot of E. Phillips Oppenheim's stuff
A couple would fit that bill:
Mr Grex of Monte Carlo (stayed up all night reading this one)
https://www.mobileread.com/forums/sho...d.php?t=148736
The Lost Ambassador
https://www.mobileread.com/forums/sho...d.php?t=148375
Probably a lot more, I've only read about 5 of them so far.