When young Per visits her uncle Sir Cumference and his family, she learns how to play the game, "Inners and Edges." After she finds a clue linking the game to the mysterious castle on the island of Immeter, she must figure out how to find the perimeter and area of a circle to unlock the island's secret. Math skills taught include finding the area and perimeter of a rectangle and a circle. Introduces an underlying concept of calculus--using straight lines to measure curves.
Sir Cumference's niece, Per, and his son, Radius, head to the Isle of Immeter where they solve riddles (and evade a sea serpent) by applying the geometric concepts of area, perimeter, and circumference. The illustrations adequately evoke medieval times, but the story drags on, and the use of made-up terms (e.g., "inners" for area) may throw readers off.