Chitral has attracted a steady trickle of travel writers and a serious anthropological literature on the Kalash. The following are worth seeking out:
Where Three Empires Meet by E. F. Knight (1893). A despatch from the Great Game era, including the Chitral campaign of 1895 — the siege of the fort and the relief column over the passes.
Wild Wales of the East is the wrong subtitle; you want The Gilgit Game by John Keay (1979), still the best single-volume history of British, Russian and Chinese moves in the western Karakoram and Hindu Kush. The Chitral chapters are excellent.
Caravans by James A. Michener (1963). A novel set in Afghanistan but with extended detours into nomadic life across the porous Chitral border. Better as a sense of place than as anthropology.
The Kalasha by Wynne Maggi (2001). A clear-eyed ethnographic account of the Kalash women of Rumbur valley; one of the best modern books on the people most travellers come to see.