From the book:

Dear Mr. Weston,
Hello again. We were beginning to wonder what had happened to you. I guess things have been pretty quiet since the Salvation Army tried to take over the world.
We are sorry, but after much deliberation we have elected not to assign any men to Protect Trillium Air Base. We feel that the Forces can protect themselves, and if they can't, who is going to protect the country?
Also, thank you for sending us that shard of broken glass with the fingerprint on it. It was yours. Our mail clerk required four stitches and a tetanus shot.
Relay our condolences to your Mr. Waghorn. We have no idea what unfortunate circumstance (for him) drew him to your ever-watchful attention, but he has no criminal record and his face is not known to us.

Hmmm, thought Sidney, Waghorn has no criminal record.
"Let me see one of those," said Tom.
"I'm sorry, Tom, but I can't show you the letters."
Tom muttered something about a lack of trust. He was extremely alarmed at the intensity of Sidney's expression. As Sidney himself would have put it, the investigation was progressing. That meant trouble. There was always trouble when his brother got to the letter-writing stage. Tom would have to stay on his toes.
Sidney opened the last letter.

Dear Mr. Weston,
Please stop bothering us.

Sidney looked up and scratched his head. It was time for him to warn the air base.

Copyright © 1982 Gordon Korman used by permission

Tom and Sidney Weston are twins on their first big summer job, working as bellhops in the prestigious Pine Grove Resort Hotel. The problem is, Sidney is convinced the Pine Grove Resort is headquarters to a massive spy ring, determined to steal all kinds of state secrets.

So while Sidney is busy collecting fingerprints, spying on the guests, and writing letters to law enforcement agencies, Tom is trying to smooth things over with the resort's manager, Mr. Parson. And while Sidney is planting bugs and mixing chemicals, Tom is trying to convince the famous artist Vishnik that the twins are not crazy, and that he shouldn't tear the hotel down brick by brick.

The amazing thing is that there is a spy operating at Pine Grove Resort ... but is it old Mr. Kitzel, who chows down on the matzo-ball soup, or Miss Fuller, who is a great friend of Sidney's? Perhaps it is TV writer Lawrence Waghorn, or athletic director Dave Bishop. Sidney is determined to find the answer, no matter what the cost.