In 1880s London, Bella Manningham is beginning to doubt her own sanity. Her husband Jack laments her lapses of memory and flights of fancy and tells her time and again that the eerie nightly dimming of the gaslight above her head is a delusion. But are Jack's unexplained disappearances from the house all in her mind as well? The arrival at the house of a retired detective named Rough signals an end to Bella's psychological torment and reveals these strange goings-on for what they really are.