In the novel Death on the Nile, Guido Richetti is an Italian archaeologist, who traveled onboard the steamer Karnak. He is described as a "slightly podgy middle-aged man".
After the Karnak arrives at Wadi Halfa, Signor Richetti insists on making an expedition of his own to a remote place called Semna. He explains that this place is of interest because it was the gateway of Nubia at the time of Amenemhet III. He offers to find a car himself, and bargains fluently in Arabic to get the car at an agreeable price.
Linnet Doyle later sees a telegram on the board, which she thinks is for her. She opens and reads it, but does not understand the message. Signor Richetti says that it is for him, and furiously snatches it from her. Linnet apologises, explaining that her name before she was married was Ridgeway, and she had not been married long, so she mistook the telegram as being for her. Signor Richetti tells her that names should be read carefully, and that it is "inexcusable to be careless in these matters".
After Linnet's death, and the discovery that her pearls are missing, all the passengers of the Karnak are searched. According to the steward, Signor Richetti creates a fuss, calling it a dishonour. Signor Richetti is also found to have a gun on him, a Mauser automatic twenty-five.
It is later revealed that he actually is an agent and criminal, and is the agitator that Colonel Race was trying to apprehend. Colonel Race had previously described him as having "five or six cold-blooded murders to his credit", and being "one of the cleverest paid agitators that ever existed". The telegram which Linnet mistakenly opened is revealed to be a coded message. According to Colonel Race, this code was used in the South African rebellion.
Poirot reveals that he always thought there was something wrong about Signor Richetti, as he was too word-perfect in his rôle, and was all archaeologist, and not enough human being.
