Together with the female spaceship Paurusheya Sigurd Westall reaches the Saturn moon Japetus. There he finds a huge moon station which is embedded in the ridges on the edge of the dark hemisphere. The station is also the destination of the alien in the small spaceship he has been following. Sigurd first tries to find his two kidnapped colleagues on his own. But when he is quickly discovered by the aliens, he is forced to defend himself. He gets help from a side that causes him to fall in the course of further action in a personal crisis.