Fantastic Voyage - Isaac Asimov

Four men and a woman are reduced to a microscopic fraction of their original size, sent in a miniaturized atomic sub through a dying man's carotid artery to destroy a blood clot in his brain. If they fail, the entire world will be doomed. \nA fabulous adventure into the last frontier of man \nAttention This is the last message you will receive until your mission is completed. You have sixty minutes once miniaturization is complete. You must be out of Benes' body before then. If not, you will return to normal size and kill Benes regardless of the success of the surgery. \n \nFour 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. \n \nTheir objective . . . to reach a blood clot and destroy it with the piercing rays of a laser. \n \nAt stake . . . the fate of the entire world.\n