The term "mysterious fire" is an idiomatic expression that refers to a situation or event that is difficult to understand, explain or predict. Full definition
Months later, mysterious fires began breaking out in piles of brick and wood from damaged buildings. (sciencemag.org)
Played by Julian Dennison, the identity of the mysterious fire - controlling mutant has remained a mystery, even as Cable (Josh Brolin) tries to kill him and Deadpool (Ryan Reynolds) assembles a whole team to protect him. (slashfilm.com)
After the loss of their parents in a mysterious fire, the three Baudelaire children face trials and tribulations attempting to uncover dark family secrets. (imdb.com)