T*A*C*K are a series of children's Mystery Fiction books from the 1980's, originally published by Scholastic and written by Marvin Miller and Nancy Robinson. Riding the wave of Encyclopedia Brown and other similar mystery and puzzle series, each book presents six or seven chapters, at the end of which the reader is invited to try and figure out the solution before seeing how it is handled.

The small town of Sandy Harbor, Connecticut is a normal, quiet coastal community. However, sometimes things happen. Problems frequently rear up, perhaps bigger than the average person can handle. Maybe even involving mysteries, or elements of danger. Enter T*A*C*K, a group of four local kids willing to lend their thinking skills to help others out. No matter the situation, be it dealing with the local bully, planning a party, or helping repair a broken lighthouse before nightfall, if the kids of T*A*C*K are involved, a solution is only minutes away.

The kids of T*A*C*K aren't Kid Detectives. Though they help in the occasional police case, they rarely ever place themselves in any direct danger. Most of the situations they deal with are struggles that are slightly out of the ordinary, enough to frustrate the people around them, but can be solved with a combination of logic and plain old common sense.

[Excerpts from TV Tropes]