Mark Tidd's Citadel, published in 1916 by Clarence Budington Kelland, is a children's adventure novel that follows Mark Tidd and his friends as they embark on a vacation at a seemingly abandoned summer hotel in Vermont. When they discover the hotel has been closed for years, they decide to rent it and take on the challenge of running it themselves. The story unfolds with the boys encountering a mystery involving a Japanese boy named Motu, who is hiding from pursuers, adding an element of intrigue to their summer escapade.
