The video focuses on the twisting story, which sees Sherlock as the prime suspect in a series of murders and Watson losing faith in his long-time friend.
The game will be played from multiple perspectives aside from Sherlock, as Watson conducts his own separate investigation to uncover clues pointing to the detective's guilt.
A third perspective will be offered as players take control of Toby, the dog from the classic Sherlock Holmes tale The Sign of Four.
Players will investigate various crime scenes and piece together clues to create their deductions, which will lead them closer to discovering the truth behind each case.
It will make use of a new high definition engine as well as intuitive new controls, allowing it to be the first of the series to release on Xbox 360 and PlayStation 3.
The Testament of Sherlock Holmes will be available in North America on PC, Xbox 360 and PlayStation 3 this September. A European date has not been confirmed by Atlus, though retailer listings in the UK also suggest a September release.