The most important fact about a Tontine is, "Who's the last person?" That is the key question in all Tontine plots. Consider, for example, a murder mystery, like Peril at Playland Isle from Detective #264. We are given the suspects and as the story evolves, each of them is eliminated logically (sometimes by being murdered) until only the guilty one is left.
The most common identifier of a Tontine-type story is the presentation of a cast of characters near the beginning:
The purpose of presenting this cast is so that the reader can go back and forth to this page at least in theory to mentally X out the innocent as their involvement is eliminated. Of course the writer (or in the story the criminal) is aware of this and so there's usually a trick in there to throw the reader off the scent.
Let's go back to the Peril at Playland Isle story. In the tale, Barden, a millionaire, has bought an amusement park and transported it to an island he owns. He is going to make admission free to kids, for reasons discussed in the panel above. But as Batman and Robin tour the site, Conn tells them that Barden wants to see them at the funhouse. When they arrive they are shocked to discover that the millionaire is dead. We learn some potential motives:
Conn is not shown as having a motive, but given that in the next scene he's attacked by the killer I think we can eliminate him. However, things change when Batman learns that a stolen necklace has been found in the park. Now he knows that the motive for the plot is not something personal, but involves other crimes that have taken place and eventually zeroes in on Carter, the business associate.
Note that a murder mystery is not the only use for a Tontine story, not by a long shot. There are several Batman stories where Bruce Wayne is in an isolated place with a few other men, and when Batman appears the other men begin eliminating suspects as to whom he is:
And the Tontine was also used in other series, like the Legion of Superheroes:
