The phrase "night is the magician" appears in Erik Larson's book "The Devil in the White City" and is used metaphorically to convey the idea that darkness, especially the cover of night, can conceal and enable various activities, both sinister and mysterious.
In the context of the book, which explores the dark and disturbing events surrounding the 1893 World's Columbian Exposition in Chicago, the phrase "night is the magician" suggests that during the nighttime, when it's harder to see and when people's guard may be down, certain nefarious deeds can take place more easily. It implies that under the cover of darkness, individuals with ill intentions can operate without as much scrutiny or visibility.
This phrase captures the essence of the book's narrative, where hidden crimes and secrets are gradually revealed against the backdrop of a grand and dazzling fair during the day, but with a much darker underbelly at night. It underscores the contrast between the public face of the fair and the hidden activities of characters like H.H. Holmes, a serial killer who used the fair as a backdrop for his crimes.