Vanishing Act of Esme Lennox

In Edinburgh in the 1930s, the Lennox family is having trouble with its youngest daughter. Esme is outspoken, unconventional and repeatedly embarrasses them in polite society. Something will have to be done. Years later, a young woman named Iris Lockhart receives a letter informing her that she has a great-aunt in a psychiatric unit who is about to be released. Iris has never heard of Esme Lennox. What could Esme have done to warrant a lifetime in an institution? And how is it possible for a person to be so completely erased from a family's history?