Whiz Tanner and the Wounded Pigeon - Tanner-Dent Mysteries, #6

It's Spring. It's Saturday. School is out in two weeks. Life is good. Joey Dent and his best friend Whiz Tanner are on a leisurely bike ride down Hyde Drive when they find an injured bird flapping in the grass beside a tree. The bird just so happens to be a carrier pigeon--wounded--by shotgun pellets. The pigeon is also carrying a mysterious coded message!The Tanner-Dent Detective Agency is in full gear, with another case to solve.  Can Agents M and K handle it, or will this case prove to be the downfall of our young heroes?And while we are asking questions...who are Agents Bluesky and Greensea?