Empire: Spiral by Tim Goff

Revised Edition! Like Game of Thrones collides with Lovecraft! Winning the demon war was one thing. Surviving the demon world is something else. A half-open portal to a demon world sits in the middle of Corber Port, the largest metropolis in the Solarian Empire. Should it fully open, the city dies. Tia Samos and her companions Sir Peter Cortez and Kyle are captives in an alien city on the Door's other side. Surviving will take everything they have. Even then, escape may be impossible. But they will try anyway… Meanwhile, Tia’s former maid Rebecca finds herself recruited into a desperate effort to seal the Door – but her allies may be as dangerous as the demons they seek to escape.