Synopsis:

While the Enterprise is cruising along it finds this black cloud thing (which is actually blue-green in color), and soon the cloud swallows the Enterprise. The being living inside it calls himself Nagilum. Nagilum puts the crew through many harmful experiments. When Nagilum says that he'll kill halkf of the Enterprise's crew, Capt. Picard sets the autodestruct sequence. When Nagilum learns of this, he sets them free becuase if the Enterprise explodes, he will die with her.