Note: Originally published in 1932 as a 5-part serial in Argosy Weekly (13 Aug), as well as in Famous Fantastic Mysteries (Feb 1941).

Synopsis: From the back cover of the Ace Books first edition: The doorway between the worlds was blocked. The mysterious room - the place where two things could occupy the same space at the same time - had been locked forever, or so its scientist guardian thought. But nobody had reckoned with the cunning brain of the ruler of that Other World, the weird warrior-king known as Bar Senestro. His advisers had also been working on the dimensional mystery, and they were ready at last. To open up The Spot of Life, to plunge through into the heart of a great American city, with an army of unearthly terrors, this was their plan. And for them, H-Hour was a matter of minutes away!