Jet-Powered Message Carrier
 
"From the paper sack he took a strange little rig.  The main part was a piece of light wood.  Taped to the bottom of it was a little aluminum cylinder.  And screwed into the top were two tiny hooks.

'What's that?' whispered Shoie.

'Don't you recognize it?  This aluminum thing is the jet engine off my model plane.  I rigged it up as a message carrier.  Give me the paper and pencil.'

On a slip of paper Alvin wrote the second message:
 

Dear Mrs. Huntley,

Attached is a piece of a pencil.  Use it to write a message on the back of this paper.  We want to know whether you are in danger.  If you are, we will call the police.  My dad is the best policeman in town.  When you have written your message, use the tape to fasten it to this jet engine.  Hook the engine back on the fishing line and give it a little shove.  It will coast back down to us.

Another Bird Lover
 

Alvin broke the tip of the pencil and carefully folded it inside the paper.  'Got to save weight,' he whispered.  'I can't send the whole pencil.'  He taped the message to the jet engine and placed the two hooks over the line so the Jet Message Carrier hung below."