In 1980, Edith Mayhew, proprietor of the Tea Planter's Club in Calcutta, is preparing to sell up after years of decline. She thinks back to 1942 when her sister Betty vanished having fled over the mountains from Burma to Assam to escape the Japanese invasion. Whilst packing, Edith comes across some letters which may hold clues to Betty's mysterious disappearance. The discovery propels Edith on an epic journey to Assam, where she is forced to face devastating secrets of love and betrayal from the war years.