A dull summer is improved when Mark, Katharine, Jane and Martha find a magic talisman, which resembles a U.S. nickel. But this particular magical money is only half magic—it cuts a wish in half and grants half of it. This causes wonderful/magical difficulty. They meet Sir Launcelot, end up with a half-talking cat, get almost kidnapped in the Sahara desert, and start their mom on a new relationship. This book is full of adventure and suspense.