The whole town of St. Petersburg is in mourning over the deaths of Tom Sawyer, Huckleberry Finn, and Joe Harper. Only they're not actually dead; they ran away to become pirates, but as they couldn't be found by a search party, it was assumed that they'd perished somewhere out there on the Mississippi.
On the day of the boys' funeral Becky Thatcher is in a particularly sorrowful mood. She has nothing to remind her of Tom, no little keepsakes to remember him by. He'd once given her his brass knob, his most treasured possession. But when Becky found out about his previous "engagement" to Amy Lawrence, she got mad at him, and gave him the brass knob back. Now she wishes she hadn't. Tom's dead—or so she thinks—and she has nothing to remember him by.