invitation. So I'm going to invite myself,
and then I'm going to invite you in here to have an ice cream soda,"
and he and Miss Nestor were soon seated at a table in a candy shop.

Tom had nearly finished his ice cream when he glanced toward the door,
and started at the sight of a man who was entering the place.

"What's the matter?" asked Mary. "Did you drop some ice cream, Tom?"

"No, Mary. But that man--"

Mary turned in time to see an excited man hurry out of the candy shop
after a hasty glance at Tom Swift.

"Who was he?" the girl asked.

"I--er--oh, some one I thought I knew, but I guess I don't," said Tom,
quickly. "Have some more cream, Mary?"

"No, thank you. Not now."

Tom was glad she did not care for any, as he was anxious to get
outside, and have a look at the man, for he thought he had recognized
the face as the same that had peered in his window. But when he and
Miss Nestor reached the front of the shop the strange man was not in
sight.

"I guess he came in to cool off after his run," mused Tom, "but when he
saw me he didn't care about it. I wonder if that was Waddington? He's a
persistent individual if it was he."

"Are you undertaking any new adventures, Tom?" asked Mary.

"Well, I'm thinking of going to Peru."

"Peru!" she cried. "Oh, what a long way to go! And when you get there
will you write to me? I'm collecting stamps, and I haven't any from
Peru."

"Is that--er--the only reason you want me to write?" asked Tom.

"No," said Mary softly, as she ran up the walk.

Tom smiled as he turned away.

Three days later he received a box from New York. It contained the
samples from the Andes tunnel, and Tom at once began his experiments to
discover a suitable explosive for rending the hard stone.

"It is compressed molten lava," said Mr. Swift. "You'll never get an
explosive that will successfully blast that, Tom."

"We'll see," declared the young inventor.

Chapter V

Mary's Present

Outside a rudely-constructed shack, in the middle of a large field,
about a mile away from the nearest of the buildings owned by Tom Swift
and his father, were gathered a group of figures one morning. From the
shack, trailing over the ground, were two insulated wires, which led to
a pile of rocks and earth some distance off. Out of the temporary
building came Koku, the giant, bearing in his arms a big rock, of
peculiar formation.

"That's it, Koku!" exclaimed Tom Swift. "Now don't drop it on