Think of One (гет)

It is an arrangement between two people who cannot be called friends - cannot be simply thought of as student and teacher - but know each other far too well to be considered mere acquaintances. There's no real label for what they are to each other - every single one Harriet tries on feels inadequate - it's all too complicated between them. But the arrangement between them, at least, is simple.
Right up until it isn't.