Culper spy ring
The bottle-cap knight can be found on page 21 of the I Spy Fantasy book.
No, Harriet the Spy is a kids book about a little girl who loves to play at being a spy and in fact does kinda spy on her friends and stuff. It is a fun book for grade school kids, but it doesn't have any fantasy elements in it.
On which page?
Smashing the Spy Ring - 1938 is rated/received certificates of: USA:Approved
I believe you want 'The Mulligan Spy Ring' .
It was a spy network in the American Revolution led by Benjamin Tallmadge.
Hoisted above in the yellow crane
A successful whaleboat raider turned spy was Caleb Brewster. He was part of the Culper spy ring.
There is a sign near the center of the spread which reads "bridge"
On the hood of the cab
Culper Ring.