Communities are the bedrock of society - physical spaces where residents share a collective purpose and common goals. But the internet has given rise to a new kind of community where lies and hate can flourish. In this episode meet a would-be utopia in Spain where civic life is managed on Twitter; a teacher who becomes the target of a digital lynch mob; and the father of a school shooting victim who must prove to the internet that his son existed.

Humans are social beings - but what happens when the emotional bonds that bind us together are threatened by forces we cannot see or touch, or worse, replaced entirely by the network? In this episode, meet a woman who has programmed her dead friend into a chat bot so he can live on forever; a Japanese family who has adopted a childlike AI robot as a member of their tribe; and a desperate mom turning to spyware to track her teenager's every move. Season finale.