The Mystery of the True Heart was an old American Girl game centered around a story about famous Burmese ruby called the True Heart. The Heart would pass through time, slipping through the fingers of anyone who tried to call it their own. The entire mystery was comprised of five total games, including bonus content. The four main games were centered around Felicity, Samantha, Kit, and Molly. After each game was completed, a code made up of three letters and numbers was given to the player. Entering all four codes unlocked the fifth game, where the final resting place of the True Heart was located. The game also provided a printable Secret Code Book where players could write codes down during gameplay.

The first game, centered around Felicity, was called The Purloined Jewel. In the game, the object was to fill a wagon by fitting different shapes together. Each time the wagon was full, a piece of a map was earned. Once all twelve map pieces were earned, the map could be put together and Felicity would figure out where the True Heart was located.

The second game, centered around Samantha, was called The Missing Heart. In the game, the object was to make chains of the colored gems. If a chain was long enough, a diamond would appear. After all of the diamonds were recovered, they formed a necklace. The final puzzle was to assemble tangram pieces to form a heart. Once that was done, then the True Heart was recovered.

The third game, centered around Kit, was called The Mystery at the Museum. In the game, the object was to move Kit through each museum room, collect a key, and open a door. To move her, blocks with the same color and symbol had to be removed. After Kit made it out of all twelve rooms, she had to solve a riddle to discover were the True Heart was hidden.

The fourth game, centered around Molly, was called The Hollywood Gem. In the game, the object was to study a dressing room for a few seconds. When the curtain dropped, an item was named and the player would click on the curtain in an attempt to find its place. After each items was discovered, a list of four suspects appeared with a word bank at the bottom. Each suspect had a fact written about them. To solve the final puzzle, the player had to match an item with each suspect, proving them innocent. Once each item was paired with each suspect correctly, the thief who stole the True Heart would appear.

Once all four final codes were collected and entered, a final game, titled The Ruby's Final Resting Place, appeared. The object of the game, set in modern times, was to match three similar pictures and clear out the board. After each level was completed, a city skyline formed at the bottom of the screen. After the skyline was fully formed, the name of the major city where the Heart was located was revealed.