On a Saturday evening in July 2017 at Panama City Beach, Florida, two young boys got caught in a powerful rip current. Before long their mother, their grandmother, and others were caught too, until nine people were struggling to stay afloat and gulping seawater. Derek Simmons and his wife Jessica, who had been having a family picnic, saw the trouble. Beachgoers started linking arms into the water, and soon about 80 strangers formed a chain stretching almost 100 yards. Simmons and his wife swam out on boogie boards and passed the swimmers back along the chain one by one. The grandmother had a heart attack in the water but survived. “It was a wave of humanity,” Simmons said.