The story centres around the life of a simple merchant's daughter, the titular Mary Marston.

Her unswerving commitment to love God and others is contrasted with a backdrop of an array of characters and a complex and sometimes mysterious plot.

The novel was written at the height of George MacDonald's literary career.

[1] MacDonald’s portrayal of the characters ranges from delightful to devious.

His message is that all eventually must stand before God, reckoning with the complicated boundaries of social class and the hypocrisy of those who call themselves Christians.