This print guide to the "XY Encounter" video offers an exciting four-part adventure about two teenage sleuths who discover the presence of an alien below New York City, and expands upon themes presented in the video. As the students try to make contact with the alien, they are confronted with a series of mathematical challenges that test their knowledge of the content strands recommended by the National Council of Teachers of Mathematics (NCTM) that include coordinate graphing, measurement and geometry, number patterns, and fractions. This guide features plot summaries, a listing of related standards, suggested video "stop" points to allow time for students to help solve the clues for finding the alien, reproducible activity sheets, and extension ideas. (ASK)