Ten Years To Doomsday

This is basically traditional old-style Campbellian science fiction, in which human ingenuity suffices to see off the nasty alien invaders. The plot shows some imagination in places, but the main problem for me is fundamental lack of plausibility.

We start with the planet of Lyff, inhabited by humans at a pre-gunpowder mediæval level of technology. With only a little help from a few emissaries from Earth, in less than ten years it's producing and manning powerful fleets of spaceships. This would be a remarkable achievement if there were some credible explanation of how it all happened; but there isn't. We're just told that it happens. Oh dear.

Apart from that, the story is pleasant and readable enough. Characterization is very slight, and the characters are male: I noticed just one named female character, who appears only briefly. Perhaps by way of compensation (?), the people of Lyff worship a female god, named Mother.