The tale of the shrinking thief

The innkeeper of a tavern had promised me some gold coins to look for a book he considered special, "King Edward part 2"; actually, the payment wasn't exactly brilliant, but I had an hour free before the Mages Guild opened, so I had plenty of time to find the volume.

I went out of the inn and began asking around. After many a talk with the townsfolk, I found a guy who advised me to speak with a lady in green (whose name now I don't remember) at a tavern nearby. She turned out to be the right person, for every gossip in the city passed through her; in fact, she knew about the book as well, and she told me that other eyes in the town were looking for it. "...and she's the person who takes things without asking, if you get my meaning!" she concluded. The opponent I was facing was a thief then. Fighting would be easy, the real problem was to find her.

Thieves are good in disappearing, but most of the time they leave traces behind them, and this particular one had made many a mistake in hiding, for I found many people in the city who knew where she could be found. It was an Emporium called something like "Theondastyr's Best Supply Shop". In some minutes walk, I was in front of its door.

I mumbled an invisibility spell and, weapon drawn, prepared to enter. That scoundrel was there, carelessly standing in front of an open door: I turned around her unseen (hehehe) and in but a moment I was behind her shoulders... but she was no longer there. Then, with my peripheral vision, I caught a glimpse of her: she had shrunk!!! I bent my head and I could see the thief in full: she was half her normal size!!! Astonished, I staggered back and I was even more amazed when I saw her grow again to her previous height!!! I began moving around, and I noticed that she changed with every single step of mine; I must have been very stealthy, though, 'cause she gave no sign of noticing me, so I took my chance: I approached cautiously and, when I was in the right spot, being her at normal size, my sword fell upon her back. I've no need to say that it was enough...

Searching the body, I easily found the book I was looking for (and obviously the innkeeper was very happy about it), but what indeed upset me was the fact that a simple thief could use a spell of "Diminution" at will, while I (proud Archmage of the Mages Guild) was not able to, even if I tried many times to customise a spell with that type of effect!