I am looking for a book that is a children/tween/teen book from the 60’s or 70’s (I borrowed it from the Bookmobile in the very early 80’s) about 3 or 4 teenagers who fly a glider and get involved in a spy plot where an organization (maybe called Chaos or similar acronym) with a plan to put a memory drug into the water supply. Originally they are set astray by misinformation that it is going into the milk supply. I think one boy is super athletic and one is the brainy one. There is one part where they fly the glider over a compound and later break in. It is guarded by a lion that has been fed the drug and doesn’t attack them but is reliving a memory. It turns out the parents of one of the kids are actually spies and assist them in the end.
Stump the Bookseller
New format, same book stumper solving.
It could be Secret Agents Four by Donald Sobol. The other possibility is a series called Christopher Cool, TEEN Agent. (Based on the CHAOS bad spy clue)
A bit of googling brought up: Secret Agents Four by Donald J. Sobol It is later than what you remember, but check it out anyhow. Everyting else fits. Cobra (not Chaos), a lion, flying, a Memory drug, a water reservoir first thought to be milk, and a spy dad.