The Clock Strikes Thirteen is one of several in the series of Penny Parker Mystery Stories by Mildred A. Wirt, most famous for writing Nancy Drew books as a ghostwriter. Sinister hooded riders are terrorizing farmers at night, and most of the farmers are reluctant to talk. Meanwhile, a man named Blake makes a generous donation to the Riverview orphan's camp and offers to buy their land, but Penny suspects that he is somehow trying to cheat the orphans. Penny Parker links the hooded bandits to Blake and prevents the orphans from being cheated.