A live WW2 hand grenade is found on the island. This leads the castaways to believe there is an enemy in their midst.

The men form a squadron led by ‘General Howell’. Soon, more hand grenades are exploded on the island and machine gun fire is also heard.

Everyone undergoes military style training – including ‘guerilla warfare tactics’ – in preparation for an attack from a still unseen, mysterious enemy.

Eventually the ‘enemy’ is revealed to be a rogue gorilla, thought to have been living on the island since WW2 and having observed humans engage in warfare.