A crate that washes ashore contains a top secret plastic explosive developed by the US Government. The Castaways make use of the plastic in a variety of objects, including nails for the Skipper, dishes for Mary Ann, jewelry for Ginger, golf balls for Mr. Howell, and even fillings for Gilligan's teeth, unaware that once hardened it becomes a dangerous explosive which will detonate on impact! (thetvdb.com)