"A reader" has already accurately summed up the novel. I will add only that The Legion of Space is an interesting read for its gender portrayals. As one would expect from the 1930s, the male characters are all obsessed with how fragile and vulnerable the heroine is; they must do whatever they can to protect her and shelter her and the thought of her in danger or even uncomfortable fills them with chauvinistic horror. Williamson allows the men to carry on this way throughout the book, all the while giving us a woman character who needs no protection whatsoever and saves the day herself. No weeping in hysterics for this heroine; Leia-like she leads the escape from the alien fortress while the men hesitate. She and she alone has the secret to the weapon of ultimate destruction, and she unhesitatingly builds it and deploys it. Not bad for 1936, eh?