Strangler's Moon — E.E. "Doc" Smith

Gone from the galaxy... A startling discovery has shaken Earth's galactic Empire: more than two hundred and fifty thousand people have vanished from the resort moon, Vesa, without a trace! Called to duty, SOTE's most daring secret agents, Jules and Yvette D'Alembert - the former aerialists from the triple-gravity planet Des Plaines, possessed of lightning-reflexes and super-strength - are faced with a lethal and baffling conspiracy.

Together the D'Alemberts have conquered many of the Empire's most dangerous foes, but now the mighty pair must divide forces - each to challenge a deadly evil terror alone!

Stranglers' Moon is the second book in the "Family D'Alembert" series.