Paul Theroux is not an author to underplay a useful motif. In the first paragraph of his new novel, we find a planeful of passengers settled down for a night flight in their sleep-masks. No sooner have they arrived at their destination – Ecuador – than the protagonist, Slade Steadman, and his lover Ava Katsina embark on an erotic game of blind man’s buff; and when, shortly afterwards, they set off along a jungle river to experience a Secoya drug ceremony, their guide insists on covering their eyes with strips of cloth.

But blindness, voluntary or involuntary, is only half of the equation in a book which veers between the inspired and the exasperating. For Theroux lack of sight is, paradoxically, a means of illumination: Steadman’s journey to the heart of darkness is also a journey to the heart of light.

Steadman is