Hidden Expedition 21: A King's Line – a story about the main character who has to protect the land in order to prove his authenticity after the repose of King Arthur. It all starts when the famous philanthropist of the Rutland family decides to build a modern laboratory and chose the site of a controversial landmark in England. The player will need to stop him from starting construction and prove that this is the authentic place where King Arthur rests.

The only difficulty the central character faces is that he will need to prove that the deceased ruler was a real person. After all, its existence comes only from legends and myths. The protagonist will have to find valuable information and communicate with those who have any information about Arthur. You have 10 in-game days to complete the task. The user needs to solve a mystery that historians cannot solve.

The strategy guide helps the gamer in difficult moments by providing hints or highlighting key elements. During the gameplay, the user will interact with the environment and try to find hidden objects. The hero communicates with the characters he meets, receiving data or instructions. The environment is filled with interactive elements and mechanisms that open doors or access other switches.