In between Adams's first trip to Madagascar with Mark Carwardine in 1985, and their series of travels that formed the basis for the radio series and non-fiction book Last Chance to See, Adams wrote two other novels with a new cast of characters. Dirk Gently's Holistic Detective Agency was first published in 1987, and was described by its author as "a kind of ghost-horror-detective-time-travel-romantic-comedy-epic, mainly concerned with mud, music and quantum mechanics". A sequel novel, The Long Dark Tea-Time of the Soul, was published a year later. In May 2002 The unfinished Salmon of Doubt was published, containing many short stories, essays, and letters. The Salmon of Doubt was originally intended to become a new Dirk Gently novel.