Chief William “Bill” Feehan kept a photo on his desk at the FDNY headquarters in Brooklyn. He and his young grandson Connor stand beaming in the photo on a fireboat in New York Harbor. The chief’s burly hands rest on Connor’s shoulders and the two brace a gust of wind that has made the boy’s hair into a wild nest. Both wear FDNY memorabilia with logos prominently displayed. The sky is a bright blue, with only a few clouds to shadow the New York City skyline. The twin towers of the World Trade Center are behind them. The fabric of the Feehan family has been closely interwoven with that of New York’s fire department for more than a century, and the journalist Brian McDonald has been entrusted with their stories. The resulting “Five Floors Up: The Heroic Family Story of Four Generations in the FDNY” is his deeply researched, intimate look into the lives of “New York’s Bravest.”