Again is an interactive crime novel about FBI special agent Jonathan Weaver, nicknamed "J". He has a special power allowing him to look into the past. He is the lone survivor of an unsolved string of murders that happened 19 years ago in Clockford, Pennsylvania, wiping out most of his family. The killer left the piece of a dollar bill that is known as the "Eye of Providence" at each scene of crime, and when very similar events start to happen again J has to use his power to unravel the mystery.
As with the other Cing games Hotel Dusk: Room 215 and Last Window: The Secret of Cape West the Nintendo DS is held sideways, like a book, during gameplay. Again uses realistic character depictions and full-motion video sequences. During conversations, one screen shows the character the player is talking to while the other is used to display clues and conversation topics. During investigations, J walks around 3-dimensional locations, controlled with the D-pad. On either screen is one version of the location, as it was in the past and as it is now. By pointing out the differences with the stylus, J gets flashbacks that show how that particular change took place, giving the player clues to what happened. This uses up psychic energy, displayed in a "psyche gauge" on screen. When the energy is depleted, the game is lost, so the player has to be careful when to use the special power. The energy automatically renews at the start of each day.