Barney and his sister Lou go to stay with their Gran over the holidays. Barney goes out to play and accidentally discovers Stig after falling down the side of the dump and through into Stig's cave. Stig and Barney instantly become friends. Just before he has to return home, Barney is given a flint by Stig. Barney's sister does not believe in Stig when Barney returns and tells them about his day. Early the next day, Lou and Gran go off to town and Barney looks in a book to check on his flint tool. He discovers that Stig is possibly from the Stone Age possibly over 30,000 years old. He goes to see Stig again, taking with him some fruit and vegetables. The two of them them work on Stig's cave as Stig is knocking out a new section at the back of the cave to make more room. Barney helps him get a chimney in place and also uses some jam jars for a window. Stig gives in an arrow head in thanks for his help. The very next day Barney finds some boys messing around at the dump, they are building some form of shed out of bits of wood and metal. Barney throws mud bombs at their little hut to try and frighten them off. The boys pretend to leave saying they have left something valuable in inside. Barney foolishly goes down and inside the hut to investigate. The boys return and capture him. Barney is introduced to The bionic man, Robin Hood, Batman and they threaten to torture him. Barney threatens them with Stig and manages to escape. The boys pursue and Stig eventually comes to the rescue and terrifies the boys. Stig takes the younger boy hostage while the older two run away. The older boys soon return with with gifts for Stig. Pretty soon all five are friends and they swear a pact never to tell anyone about Stig.