Henry asked his grandmother to go on a wilderness adventure in the woods near her house. They gathered supplies like a guidebook, telescope, and bug catching equipment. Henry's grandmother read the rules of the trip to stay safe. They told Henry's grandfather and dog Felix they were leaving. Along the way, they crossed wooden planks over a canyon and climbed a wall. Henry's grandmother warned about poison ivy. They got lost until finding a neighbor's swimming pool. They thought they saw a pony but it was Henry's grandfather and dog waiting for them. They returned safely after Henry got bit by a mosquito but wasn't poisoned by ivy.