Artemis 81 (1981)

Paranormal novelist Gideon Harlax is drawn into a battle between the forces of good, represented by alien angel Helith, and the forces of evil, represented by Helith's evil brother Asrael. Ranging from Oxford to Denmark, a North Sea ferry to an alien planet, Harlax unwittingly becomes part of an ancient plot that may result in the destruction of Earth...