Imperial Stars by E.E. "Doc" Smith and Stephen Goldin

A fair amount of time ago (pre-Amazon), I was reading and collecting the Family d'Alembert series written by "Doc" Smith (edited and finished by Goldin and published by his wife after his passing, I believe), and eventually just lost track of the progress of the series, so I missed the last few, which I didn't find out until I was playing around on Goodreads a month or so ago. I got lucky and found a source for a bunch of old SF ebooks, and all of the series was there, as well as his Lensman and Galactic Patrol stuff, which I've had in paperback for years. So, after so much time has passed, one can't just jump in at the end of the series and read the last ones, and I had to start at the beginning, with Imperial Stars.

It's difficult to say, at this point, so far removed from the time in which it was written, but there may be a bit more than just a bit of satire in this story, containing elements of the Bond mythos, some very broad space opera, and a pair of heroes who are trapeze artists from a long line of circus folks. Here in book 1, the Empire is threatened by the plotting of a pretender to the throne, the bastard cousin of the current Emperor Stanley. The bastard has possession of a patent acknowledging his parentage and nobility, and many good secret agents in the SOTE (Service of the Empire) have died trying to recover the document. At last, the Head of SOTE is down to his ultimate weapon, Jules and Yvette d'Alembert, performers in galaxy-renowned Circus of the Galaxy, where for generations the top agents of SOTE have trained in secret.

Jules and Yvette and their family come from the triple-gravity planet of DesPlaines, so they are far faster and stronger than ordinary humans, and their training has made them the most deadly creatures in the galaxy. They go undercover on several worlds to uncover the conspiracy and to foil the plots of the evil bastard, far too handily for serious fiction, but in an amusing and overblown and heroic fashion all the same. A fun little mindless tale that broke me out of my slump at last.