Max is horrified when he is invited to participate in the Duke of Wellington awards involving four days of cycling and camping in the woods. Luckily his friends agree to join in and very soon Lucy, Max, Charlie, Joe and Sherlock set off together for a cycling trip in the marshes. But the gang can't stay away from adventures for long and when they meet a young American boy named Byron, they are faced with their biggest puzzle yet. Just what are the mysterious lights they see hovering above the marshes? Why is Byron's father so wary of strangers? And what secrets is the sinister housekeeper hinding?