The Reverend Mother is delighted with her new entrant to the convent. Young Sister Gertrude is well-educated, has worked for an accountant and has an appealing sense of humour. But one autumn morning, Sister Gertrude is found dead inside a small wooden shed, just beside the river. Surely a young nun could not die from alcohol poisoning?

But when the Reverend Mother delves more deeply into Sister Gertrude's background, she finds some puzzling anomalies. Why did the young nun not delay her entry to the convent until after her sister's wedding? Is it a coincidence that her father died of a similar illness not long before? And could there be a link between Sister Gertrude's death and the gunpowder explosion on Spike Island? The Reverend Mother must find the answers to these questions if she is to safeguard her community from suspicions of murder.