the glass doors slid open and i darted through them just as liz said , `` okay , '' but i could n't stop moving , did n't dare break my pace until i reached the supply closet in the east corridor , where i slid aside a stack of long fluorescent light-bulbs , grabbed a flashlight from the top shelf , and found the loose stone that i had discovered one day during my seventh-grade year while looking for onyx , buckingham 's cat .