Kids Book in the 80's in the US... kids club has cool treehouse and everyone wears superhero costume

[soulsinging]

I'm looking for a book I recall from my childhood about a group of kids that have some sort of club. They all wear costumes for superheros (there's a batman/robin duo, a wonder woman, etc) and they have a really awesome treehouse, cars, etc. In the book I remember, their "case" is finding a lost dog and one of their tactics is to use a dog whistle that brings every dog in town running to them.

This is a real long shot, as nobody in my family seems to remember this one and I know we all read it 100 times...

 

[Jd123]

Did you ever figure out the book? I've been looking too

 

[otistdog]

@Jd123, if you can add any details that the original poster didn't include, that would improve the chance of the story being found.

 

[soulsinging]

Did you ever figure out the book? I've been looking too

I did not. Pretty sure the dog's name was chocolate. I doubt it's in print, I feel like the licensing would have become prohibitive.