Dauntless by Lisa Henry

Welcome to Dauntless Island, where nothing much has changed in two hundred years, and that’s just how the islanders like it.

Joe Nesmith leads a peaceful life as the lighthouse keeper on Dauntless Island, a small community off the coast of Australia where the occupants are proud of their mutinous history and have very long memories.
When graduate student Eddie Hawthorne comes to Dauntless, he brings with him a historical diary that throws everything the islanders have ever believed into disarray—and one of them may even resort to deadly measures to make sure that Eddie’s research never sees the light of day.
Unless Joe and Eddie can stop it, Dauntless’s bloody history is set to repeat itself. On the plus side, if they survive this, they might actually realise they’re falling in love.

Dauntless contains a taciturn lighthouse keeper, a cute history nerd, a dog who thinks she’s a seal, and a diary that’s apparently worth killing for. Also, watch out for the goats.