Seneca Falls police are investigating an armed robbery. A man walked into McDonald's at about 11 o'clock Wednesday night, displayed a gun and demanded money from the cash register. The suspect then ran away. He's described as a white man with a slender build in his late teens to early 20s. He was wearing a dark colored Hollister hooded sweatshirt, jeans, dark colored shoes with white trim and a Yankees hat. If you have any information, call Seneca Falls police at 568-4850.