Four friends - a doctor, an architect who has built the machine, a geologist and a jurist - ride a cube-shaped car driven by repelling currents to Mercury, a dead-looking world that turns out to hold the remains of a civilisation and its ruler, and go on to Venus, where they are sure a people once lived as well. Flint wrote it for the pulp magazines in 1919, and the pleasure is in the travellers arguing over what they find: each planet a thought experiment about how a society might be organised and what it might cost. Fifty-six plates of moonlit harbours, castles and volcanoes by Munch and Dahl carry the same strange light the travellers find on Mercury and Venus.