When three white horses mysteriously appear in the fictitious Cornish village of St Gweep, various theories start doing the rounds among both the locals and the tourists.

Meanwhile Mary is doing her best to seduce PC Allan giving villagers reason to gossip about the state of her dwindling relationship with her partner Angela. However, Mary's plans for romancing the lovable PC go astray when he decides to ask Holly out on a date.

By way of distraction Mary takes up some serious reading and creates a book corner in her shop which turns out to be about as successful as her plans to woo PC Allan.