One night many years ago, Ed Spencer, a student at a seminary near Lake Michigan, was awakened by shouts that there had been a shipwreck offshore from the campus. An excursion boat from the nearby Chicago harbor had collided with a freighter and was sinking. Spencer ran down to the lakeshore from which he could see lights from the boats. A strong swimmer, he plunged into the icy water and started searching for survivors.

For six hours Spencer swam out and back, pulling people ashore, battling stormy waves and powerful undertow. By dawn, he had personally rescued 15 people in as many trips. Exhausted, he sat down until someone spotted two more still in the water. Spencer dove in again and found a man and a woman clinging desperately to a piece of wreckage. He brought them in, too, and coll…