HOPEWELL, Mo. • William Helms was building a shed for his farm. Needing one more board, he went to fetch a discarded plank near the railroad bridge over the Big River in Washington County. The Iron Mountain Railroad’s passenger train No. 4 rumbled over the bridge, bound for St. Louis 65 miles to the north. Helms was walking the track through a low rock cut when he heard a strange squeak, like that of a field mouse. He saw a small, battered piece of luggage. “I opened it, and inside was a baby,” said Helms.