Sentinel — S.A. Pavli

When a giant alien spaceship suddenly appeared parked next to the International Space Station, the world was agog with disbelief that alien first contact had actually happened. But then the spaceship left and another different alien spaceship arrived. The Earth was precipitated into an interstellar war between two powerful advanced civilisations, without knowing which one to trust. Only one man knew what was happening; ex-RAF pilot Captain Willian Morgan, but he was treated as a crank by Earth's leaders. The Captain found himself on the front line of an interstellar war that threatened the very existence of human life on Earth.