The main challenge that Percy and his friends, Grover and Annabeth, face is the mattress store owner, Crusty, and his plot. Crusty is short for Procrustes, which in and of itself gives us an idea of what the problem is. Procrustes was a figure in ancient Greek myth who was insistent on fitting people to a bed he had; if they were too short, he would stretch them out to fit the bed perfectly, and if they were too tall, he would cut parts of them off. This is precisely what he was doing in chapter 17 of The Lightning Thief. Grover and Annabeth were tricked into getting into some of the beds, but before Crusty could do anything to them, Percy tricked him into falling into his own trap. This is very much like what Theseus had done to Procrustes when he faced the man on his way to Athens. In the end, Grover and Annabeth were freed, and they and Percy left in safety to continue on their adventure to the Underworld.