Who Really Killed Cock Robin: An Ecological Mystery by Jean Craighead George published by HarperCollins, 1971, 1991.
Obviously, an environmental message is the cornerstone of this novel. The story is told in third person and follows Tony Isidoro, an eighth grader who has been recruited by the Mayor to solve the mystery of a robin's death. The plot includes politics and corporate interests, along with a hint of government conspiracy. Tony has become interested in bird watching in the absence of his brother Izzy who had been working on a graduate thesis about the local robins before he was drafted into the Army. Tony is invested in this mystery because his brother has asked him to continue his observations. From the time it was written, we can infer that Izzy is likely in Vietnam. But it feels more like he is away at college somewhere instead of in a potentially life-threatening situation. Tony seems much more worried about the environmental impact of the local toxins than about his brother.
But, there are many notable scenes. Tony defies the Mayor and exhumes the robin's corpse following a small funeral. At the end of chapter six, the reader is reassured that Tony is actually a kid when he convinces Mary Alice to go fishing. In this scene, George finesses the environmental information into the story subtly.
This classic is a must-read for all budding environmentalists.