Snoopy finds himself almost completely engrossed in his persona as the World War I Flying Ace -- to the point where he goes to camp with Charlie Brown and maintains his persona throughout the entire two-week period (much to Peppermint Patty's bafflement).
Still, Snoopy looms large, so this volume (a particularly Snoopy-heavy one) sees him arm-wrestling Lucy as the "Masked Marvel" and then taking off for Petaluma for the national arm-wrestling...