Phytosphere

When the alien Tarsalans mount a light-blocking sphere around Earth to further their aims of conquest, two scientists race against time to destroy it, even as crops die in the endless night of the phytosphere, and famine and anarchy tighten their hold on civilization. Matters go from bad to worse when Earth's over-zealous military, seeking to defeat the Tarsalans, inadvertently destroy the phytosphere's control mechanism, turning it into a train without brakes. One of the scientists fails to destroy the light-blocking sphere. This leaves it up to the remaining scientist. But he is on an isolated moon community without resources or weapons, and must use only his wits and cunning to defeat the twin-brained super-intelligent Tarsalans. Alien-based post-apocalyptic fiction at its best!