From the back of the package: An incredible medical journey is about to begin. You and your submarine are to be reduced to microscopic proportions and injected into the bloodstream of a critically ill patient. Your mission is to navigate through a narrow network of veins and destroy a life threatening blood clot located near the patient's brain. Defense cells, bacteria, antibodies and enzymes are only a few of the strange obstacles you will find along the way. Blast your way through them and save the patient's life. Prepare yourself for one Fantastic Journey!