[1] The book is an expansion of the author's novella "The Onslaught from Rigel," originally published in the magazine Wonder Stories Quarterly in the issue for Winter 1932.

The militaristic Lassans believe it their destiny to destroy or enslave all "lesser" beings and accordingly plan to capture those who have survived their initial strike.

Ruby's group is relieved by a warship from Australia, whose inhabitants have been less affected by the Lassan radiation—in their case, it has merely turned the iron in their blood to cobalt, rendering them blue-skinned.

"[4] Rating the book two stars out of five, Floyd C. Gale in Galaxy Science Fiction wrote in 1961 "[e]ven when I first read the magazine version as a lad back in '31, the story seemed utterly improbable.

He felt "the Rigellians behave with unbelievable stupidity and the metal humans with their built-in stiff upper lips are too flip and glib," concluding that "Pratt's reputation rests secure on much better ground than this bog.