I've read a couple of the Dr. Palfrey books. He was at one time an agent of Dept. Z but leaves that spy world in the series that features him as the lead character. They're like protoytpes of The X Files with lots of bizarre sci-fi elements. Almost as if Sax Rohmer decided to write about master criminals who used horrors of science instead of occult powers in their attempt to take over the world.
The Dr. Palfrey series is one of the two "major" series by John Creasey that I've never sampled (the other being George Gideon). That might change in the near future as I did pick up some Palfrey novels with great cover art (I smell a teaser!).
I remember reading a Dr Palfrey novel in the 70s because it had the same cover illustrator as Doc Savage!