Tale of Four Planets

Earthlings prepare for interplanetary war against hunger-crazed deerlike creatures from the planet Tictoctic. However, mobile telepathic trees from the planet Oomb have persuaded the captain of starship Smoke and Mirrors to give peace a chance, flying into the heart of the Tictoctic Empire totally defenseless. Are they too naïve for their own good? Will faithless scheming sabotage their plans? Will the Watchers intervene?
One civilization has already been destroyed. The fate of three others hangs in the balance.