Mad Scientists? -or Historians? I really liked the dry humour of this one. Instead of mad scientists we get mad historians with time machines, equally able to make things go bang, and living proof that no battle plan _ever_ survives contact with ... reality.
Style-wise it reminded me of Eric Frank Russell, especially his "Men, Martians and Machines", and perhaps Harry Harrison (Bill, the Galactic Hero).
It took a while to get through the scene-setting and into some genuine "adventures". I did wonder if it was going to turn into something like Larry Niven's The Flight of the Horse - a succession of themed tales tied together by a technology, some characters and the author's desire to spin some time travel yarns with a bet-you-didn't-see-that-coming ending to each.
But then it changed, and I realised the body count was climbing, and there seemed to be a darker force at work.
At that point I started to read faster, because I was enjoying the story, and that may have been a mistake. I lost track of who the male leads were - I'd been sure the main (female) protag seemed to be involved with just one of them, but I'd forgotten which.
There was the Boss and the Chief - and I think I got it straightened out their respective ranks and specialities, and a variety of characters with names beginning with M. Then the body count climbed further and we suddenly got non-historians roped in, and every male just became a potential redshirt.
An early plot device - the space-time continuum's ability to drop large blocks of stone on top of any historian who threatened to disturb the established timeline - just disappeared in the second half of the book, when it would have become way too inconvenient and would have seriously impeded both the booming villainy and also the heroes' attempts to thwart it.
I loved the story and the style, but the redshirt-nature of the male characters and the lack of rigour to the rules of time travel lose a star and a half.
I shall most likely read the next book in the series.