From Book Two: The Cheerful Thief

First passage:
 

"I promise you there is no gambling involved," Lady Mizar replied. "Torch, would you like to try your luck?"

Torch took the dice to the table in the centre of the room. Brother Timothy followed. Glancing at Lady Mizar, Torch shook the dice in his fist and rolled them out on the tablecloth. He rolled a five and a two, a total of seven.

"Lucky dice," he said. He rolled again. This time he got a five and a six, for eleven. "Very lucky dice." He rolled six more times and always got either seven or eleven.

"How does it work?" Torch asked. "It has to be a trick." He held the dice up to the flame of the lamp, looking for weights or bubbles inside the transparent cubes. He thought he saw a couple of gnats trapped inside the amber, but there was no sign of tampering.

"Most certainly it is a trick," replied the sorceress, "but how it works is for you to find out. You may keep the dice until you solve the mystery."

"How long will that be?" he asked.

"Not long," she smiled. "Have faith."
 

Some Time Later...

Torch glanced out the window again. Nothing new.
 

He looked down at the two yellow dice on the ledge. They mocked him. How could they always roll seven and eleven? For the hundredth time, he lifted the dice and held them to the light. There was no sign of tampering. The dice should roll true, and yet they didn't. He put them down.

What had Mizar said about the dice? Give people something interesting to look at, and they will miss the obvious thing right next to it. Idly, he tipped one of the dice with his finger. Five. He tipped it over again. Five. He frowned. He tipped it over to a fresh side. Five. He picked up the die and examined the outside instead of peering into the interior. There were five spots on every side.

"Damn," he said.

The other die was more complicated. Three of the sides each had two spots painted on them. The other three sides sported six spots.

One die had to roll five because that's all it could do. The other rolled either two or six, for a total of seven or eleven.

"Damn," he said. He felt like a fool. How many times had he looked at those dice?

Give a man a pair of transparent dice, and he will look inside them instead of noticing the obvious spots on the outside.

Torch looked up and caught Father Timothy watching him. The friar smiled and winked.