Asimov

Four men and one woman reduced to a microscopic fraction of their original size, boarding a miniaturized atomic sub and being injected into a dying man’s carotid artery. Passing through the heart, entering the inner ear where even the slightest sound would destroy them, battling relentlessly into the cranium. Their objective . . . to reach a blood clot and destroy it with the piercing rays of a laser. At stake . . . the fate of the entire world.