Don't know whay this is so cheap - may be a mis-price, so if you are interested, get it while you can. It is currently around and over £10 everywhere else... It contains a few pretty good episodes from the "William" story arc, which is one of the ongoing plots in the series.
Details: At FBI Headquarters, Agent Scully is summoned to Deputy Director Kersh's office to identify a collection of strange symbolic rubbings. Although Kersh refuses to discuss the rubbings, Scully secretly thinks they are from a spacecraft found off the coast of Africa two years earlier. When Agent Reyes and Agent Doggett discover the rubbings are from a second spacecraft, Scully is convinced the symbols provide answers about the existence of her son, William - a belief that is frighteningly confirmed when William is kidnapped by a UFO cult that also believes in an unearthly connection between spacecraft and child.