Twenty-fourth Level is a mystery novel by Kenneth Benton set in Brazil in the 1960s.

Overseas Police Adviser Peter Craig interviews a Rio, Brazil diamond dealer to investigate the source of unusual stone samples that have appeared at the International Diamond Institute in London.

In the course of a social engagement, Craig encounters and quarrels with Graben, a violent and corrupt engineer that he arrested while working in West Africa.

The investigation leads into a nearby favela, then to a gold mine near Belo Horizonte, which is owned by Alcidia's father.

Craig manages to kill Jair and returns to the mine hospital with letters that prove Graben's guilt.