Anthony Marston uses a simile that ironically compares the situation on Soldier Island to a “detective story” due to the mysterious absence of their host, Mr. Owen, and a gramophone recording that accuses the guests of a series of murders. The narrator describes the comments of Justice Wargrave, who proposes that they all leave the island as soon as possible, and Marston, who is, in contrast, excited by the surprising turn of events: 

“Then in my opinion it would be well if we all left tomorrow morning as soon as Narracott’s boat arrives.” 

There was a chorus of agreement with only one dissentient voice. It was Anthony Marston who disagreed with the majority. 

“A bit unsporting, what?” he said. “Ought to ferret out the mystery before we go. Whole thing’s like a detective story. Positively thrilling.” 

The judge said acidly: “At my time of life, I have no desire for ‘thrills’ as you call them.” 

Anthony said with a grin: “The legal life’s narrowing! I’m all for crime! Here’s to it.”

Though Wargrave feels that it might be dangerous to stay on the island, Marston feels that it would be “unsporting” to leave before they have solved the “mystery” posed by their unknown host. In a simile, he describes their enigmatic and sensational circumstances as being “like a detective story,” which he finds “positively thrilling.” There is a pointed sense of irony in his use of this simile, as And Then There Were None is in fact an example of mystery or “detective” fiction. Marston's comment, then, is surprisingly astute.