Tense

Tense, a logical, rational engineer and atheist, meets Sally, an Angel, or possibly an escaped, psychotic mental patient.
Over the next seven days, Tense and Sally fall in love, discuss existential philosophy, eat (a lot), discover sex, and fend off Sally's psychiatrist (or is he really Lucifer?).
Lucifer (or is he really Sally's psychiatrist?) wants Sally, who may be Amitiel, Angel of Truth, to support his ongoing war on God. Sally doesn't really want to.
What could possibly go wrong?