How did the professor stumble upon the Egypt game?

The
professor stumbled upon the Egypt Game while looking for something in a storeroom in the back of
his antique shop. 

Since he was not used to being in the storeroom, his
curiosity was piqued when he heard a noise coming from outside the storeroom. The text tells us
that the storeroom overlooked an abandoned yard surrounded by a fence and that there was a
dilapidated lean-to shed in the yard. 

Since the storeroom window was caked
with grime, the professor had to rub out a spot in the thick coating of dirt before he could
look through the glass. As he looked through the...