Being the skipper of the cutter that carries all supplies and communications between Tasmania and Maria Island is a powerful position - and a deadly one. 

Monsarrat and Mrs Mulrooney are sent to Maria Island in January of 1826, the very early days of the penal settlement there, to solve the murder of Harefield - the man who sailed the government cutter between mainland Tasmania and Maria Island, bringing all supplies and correspondence and directives - all of which he made sure to read. Knowledge is currency. 

One of Harefield's other responsibilities was to light the primitive lighthouse to keep the whaling boats out to sea safe. During a storm, Harefield was shaken from a ladder whilst igniting the light. He was then attacked with an axe, falling over the cliff edge to his death. 

All blame is laid at the feet of Thomas Power, the charismatic Irish revolutionary held in detention - with a lot of privileges - on Maria Island. But did he do it? The outsiders, Monsarrat and Mrs Mulrooney, are brought in to deescalate gossip and surmise. 

Power has continued to smuggle his writings out to the British press throughout his internment, and the government does not want him gaining further attention. But did the no-doubt troublemaking, charismatic, educated and charming Power sink to the low of murder to prevent the unscrupulous Harefield from blackmailing him? Or were there others who had reason to want Harefield shut up?