The crew of the Aniran spaceship dies after encountering an absolutely inexplicable phenomenon in space. He will be called the Lord of Darkness - an abstract and formless evil, a substance that has concentrated in itself all the horror and all the hatred of the Universe... An employee of the earth's special service, Captain Arlan Zaslavsky, after his retirement, has little in common with his native planet - he is alone and does not owe anything to anyone. Therefore, he easily agrees to sign a rather strange contract with the Anirans for twenty long years. Possessing a unique property - immunity to the deadly “D-radiation”, capable of destroying entire worlds, Captain Zaslavsky becomes the last hope of humanity and the first of those who in legends are called “Sentries of the Universe”.