Aboard a yacht anchored in the Thames Estuary five men are waiting for the tide to turn.

Among them is Marlow, who reflects on what Roman invaders must have felt as they arrived in that very spot, when it was `one of the dark places of the earth'.

His mind turns to a past experience and a journey into a different wilderness.

So begins Marlow's tale of a young steamboat captain employed by a Continental trading company with business interests in Africa.

When he arrives at the colonial outpost, Marlow witnesses the rapacious greed of the ivory traders and the brutal exploitation of the natives.

He also hears of the enigmatic Mr Kurtz, the company's top agent based deep in the interior, who is said to have fallen ill.

Marlow is filled with growing unease as he journeys upriver, where he discovers the harrowing truth underpinning Kurtz's elevated status and high reputation.

Heart of Darkness is a haunting nightmare, a journey into the darkest reaches of man's soul exposing the venality and baseness lurking beneath the veneer of civilisation.

Its sombre theme, said Conrad, necessitated that he endow the story with `a sinister resonance, a tonality of its own, a continued vibration that, I hoped, would hang in the air and dwell on the ear after the last note had been struck'.