A baffling alert. A race to the wrong building. Notre-Dame still stands only because firefighters decided to risk everything. The security employee monitoring the smoke alarm panel at Notre-Dame cathedral was just three days on the job when the red warning light flashed on the evening of April 15: “Feu.” Fire.

It was 6:18 on a Monday, the week before Easter. The Rev. Jean-Pierre Caveau was celebrating Mass before hundreds of worshipers and visitors, and the employee radioed a church guard who was standing just a few feet from the altar.

Go check for fire, the guard was told. He did and found nothing.

It took nearly 30 minutes before they realized their mistake: The guard had gone to the wrong building. The fire was in the attic of the cathedral, the famed latticework of ancient timbers known as “the forest.”... [+]