DinerTown Detective Agency is a hidden object spin-off of the Diner Dash series of games, with the same characters and some adventure elements. Bernie decides to become a private investigator after reading an advertising for a detective kit from a magazine. Joining forces with his friend Flo, he starts to investigate strange disappearances, acts of vandalism and thefts around the town. The game can be played with or without a time limit for each chapter, be selecting one of two modes at the beginning.
Each chapter is a crime to be solved, following the cartoon theme of the game with wacky motives and no graphic violence. Most of the time, the objective is to collect all the items from a notepad list at the left side of the screen, on crime scenes cluttered with assorted paraphernalia. Besides searching the screen carefully, finding and clicking on all the required objects, the player has to use a special tool below the notepad to gather some clues, marked with icons on the list. The tools are forensic equipment, like magnifying glasses, fingerprint powder and substance reagents. The hint button sitting at the bottom of the list highlights the position of one of the required items, but takes some time to recharge after use.
In some scenes, the goal is to pick up all the pieces of a segmented object, then drag and drop it from the notepad to a logical part of the scenery to solve puzzles. For example, assembling all the broken shards of a smashed mirror to place them back to the frame. Some locations have special puzzles that take place on a separate screen, shimmering on parts of the scenery to indicate their presence. These puzzles are self-contained mini-games, with jigsaw puzzles, matching fingerprints to suspects, arranging cards in logical sequences and similar challenges.
At the end of each investigation, the player has to find the culprit from three suspects, by reading the testimony clues of nine witnesses and using this information to mark three cards with false or positive answers to the three theory questions. The guilty card has to match the theory answers, shown at the top of the screen with characteristics of the criminal, like favorite color, other personal tastes and life history.