This collection differs significantly from the overwhelming majority of the tête-bêche Ace Doubles publications. Whereas most of them contain two novels, this one consists of a novel and a quartet of short stories. Eric Frank Russell looms large in it, as not only is he the author of the novel Sentinels in Space, but his is the first story of the four in the reverse-ended collection of tales.

Unfortunately this isn't to Russell's advantage. Every one of his works that I have encountered are centered around superbeings who step in and deal with some powerful foe that threatens peace or freedom or whatnot, and the combination here brings the repetition into sharp relief. In the case of Sentinels of Space Russell spins an entertaining tale in which the nature of the superbeings in his tale is itself a mystery that Russell develops as they set themselves to head off the threat of war between the Earth and factions on the human colonies on Mars and Venus. It's fairly suspenseful and engaging enough to propel the reader right through to the end. By contrast, the premise in the namesake novella in the short-story collection possesses none of the narrative tension, as the protagonist never seems in danger or even at risk of failing in his mission. In that case, Russell's formula failed to produce a decent story.

Fortunately the reading effort is redeemed by the other stories. My favorite of the four was Malcolm Jameson's "The Alien Envoy," in which extraterrestrials who have occupied the gas giants in the solar system reach out to humans to establish peace. It's an effective antidote to Russell's tepid tale in a lot of respects, and has an ending that I found touching. I found Murray Leinster's "The Malignant Marauder" to be just as enjoyable, as it's a refreshing time travel story that works pretty well. The same cannot be said for Frank Belknap Long's "The Temporal Transgressor," which I thought was under-plotted and over-written. It's the first of his stories that I can recall encountering, and it didn't leave me with much of a desire to seek out his others. ( )