In To Defend the Earth we didn't go much into the Alien Jai invaders. Who were they? What did they think of all this? With To Survive the Earth we answered some of those questions.
In the story, Craziest Ivan, a Russian naval captain is captured by the Jai after the former's failed attack on Jai occupied Venus. Our captured Russian learns something of the Jai home system, three inhabitable worlds, their history, and even sees some of their cinema. Everyone gets very friendly....for a while.