"I don't know," replied my patient with a frown.

"Well, there's one way to find out," I said cheerily, cutting across the slight embarrassment I could see rising in my wife's cheeks at the feeling that she had committed a faux pas. I seated the ladies at the little table and dug out a card deck from the secretary desk. "If you can't remember a game, we'll teach you one," I said, handing her the deck. "See if something comes back to you."

She took the cards and held them in her hands a moment, as if weighing them. Then she cut them and began to shuffle. In spite of a certain stiffness from her injury, they whirred, blurred in her hands. A sudden grin passed over her face, like a patch of sunlight over a distant hillside on a cloudy day.

"I don't remember a game, but I remember some card tricks." She eyed my wife a moment as if sizing her up. "Place your hands upon the table," she commanded Alicia, "and I will show you the even-odd trick."

I nodded reassuringly at Alicia's questioning glance, and she placed her palms down upon the table.

"Now, pick a small, even number," my patient continued. "Two?"

"Fine. Now I will place two cards between each of your fingers. An even number, you see, between each finger-we count the thumb as a finger-of each hand. But between the last two fingers we place an odd card, one card. Now," she went on with easy, cheerful assurance, "I shall take each pair of cards from between your fingers and put them into two even piles. An even number of cards divided evenly into even piles. Now take the last card, the odd card that is left in your hand, and make one of the even piles odd."

My wife complied with a polite, bewildered smile. I suddenly realized that my nearly two decades of climbing the seventeen steps to 22IB Baker Street had not been entirely profitless for my mental faculties.