Mr. Ratburn assigns Arthur's class to write letters to another third grade class in another school.  He explains that these students will be their pen pals and since their pen pals don't know anything about them, they need to write something a letter about themselves. Arthur isn't sure what to tell a stranger --- he wants make himself sound interesting. So Arthur exaggerates his basketball abilities to make it sound like he's a great player.

Later, Arthur admits to his friends that he stretched the truth a bit, but what difference does it make, right? His pen pal will never know the difference. But Justin, his pen pal, turns out to be Mrs. MacGrady's grandson, and she arranges for the boys to meet. With only two days until Justin arrives, can Arthur's friends teach him to be the ball player he claims to be?