Dr Euan Magnus Campbell Gregory, minister and chaplain at St Giles College, Glasgow University, meets Isla Taylor, a married woman, soprano, classical pianist and teacher, in church one afternoon during a Christmas concert.
They converse for a few moments.
Nine months later, their paths cross again.
Messenger takes over their lives when they cannot meet face to face.
It is only when they stop messaging one another that they realise what is real and what is fantasy.
Where will their adventure end?