Book 1

Secret of Terror Castle

by Robert Arthur

Published October 1967

Book 2


Book 3

Three young detectives undertake a case involving an Egyptian mummy that whispers, but only to one man.

Book 4

Mystery of the Green Ghost

by Robert Arthur

Published 1 October 1965

Book 5

The three investigators take on two mysteries: the disappearance of an ancient jeweled Japanese belt from a museum exhibit and the strange antics of a group of gnomes around an elderly woman's house.

Book 6

Secret of Skeleton Island

by Robert Arthur

Published 27 July 1970
The Three Investigators are assisted by a Greek youth as they search for clues to a mysterious thief on an island once inhabited by pirates.

Book 9


Book 11


Three young detectives travel abroad to solve a mystery involving a silver spider and a political plot that endangers the life of a young prince.

Mystery of the Fiery Eye

by Robert Arthur

Published September 1969
Three junior detectives solve a mystery involving a collection of antique busts, a legacy, a strange letter, and a red ruby.