Travelling sometimes with his pet tui, which both elevates and irritates him, Ernst meets Te Rauparaha, travels to Port Nicholson where the sails of whaling ships shine like moth wings, climbs Mt Egmont (remember that ugly, abject name?) on the second attempt, drinks a few bottles of Porirua Lightnin', searches for the slave girl Hariata.
Conroy presents Dieffenbach as one of those early 19th century polymaths, convinced that energy and application could make them master of any scientific discipline. He's an endearingly assiduous note-taker, in his "sleek longhand", recording Te Rauparaha's lament, collecting folk tales in England, observing wince-making surgery in Berlin, boiling water on a mountain summit to estimate the height.
He's liberal and clear-eyed in his awareness of the cultural confrontations he's witnessing. Maori recognise that their earth is shifting, and Dieffenbach wonders whether the European presence will bring peace or subordination. "Can a new kind of colony be founded between two peoples so much at odds?"
It's a dilemma that Conroy renders deftly through actions and utterances from both sides.
There are a few places where information sits like a rock in a river. Rather a lot of contemporary writers are quoted, usually pertinently. Rather a lot of contemporary figures - Cook, Charles Lyell, Worse Heberly, Dicky Barrett - are mentioned, usually appropriately.
The story takes Dieffenbach back home, in an effectively subdued ending of memories and mortality.
Thom Conroy has already published a lot of shorter fiction, and won awards with it. He's put in the writer's kilometres, and The Naturalist's measured, lucid style shows this.
The Naturalist by Thom Conroy (Vintage $37.99).