that the people could make themselves invisible?"

"That's where the real story comes in," his mother explained. "You know
there is a long passageway between the front rooms of the Fernbloms and
their kitchen in the rear. It runs back of the stairs. The next time you
go through it, stamp your foot very hard, and you will hear that it
sounds hollow in one place. At that spot there used to be a trap door in
the floor. Now it is nailed down hard, but in the old days it could be
opened any time, and then you found a stairway below. It led into our
part of the cellar, where you still can find a couple of stone steps at
one end. Then the conspirators went down into the main cellar, and at
the back of it there was a tunnel leading under the rear part of the
house and the lane beyond to a house on the other side. That's the way
they escaped, and that's why the police never found anybody in
the club."

"What did the conspirators want," asked Keith after he had pondered the
matter for a while.

"I don't know exactly," his mother admitted, "but the king was killed by
one of them at last."

"I wish I had been there to defend the king," said Keith. Then a new
thought seized him suddenly: "I want to go down and see those steps."

"All right," his mother answered to his astonishment and joy. "Lena will
soon go down to get potatoes for dinner, and then you can go along, if
you only promise to come right up again."

Shortly afterwards the momentous expedition actually took place. Keith