Season 3, episode 3 discussion here.

Where to begin? Let's start back with Niagara Falls, 1981, as we follow the story of Kevin Garvey Sr: past and present.

So Kevin Garvey Sr. lost his wife to cancer around 1981, and went on a roadtrip with Kevin Garvey Jr, who was eight years old at the time, during the summer. Kevin Garvey Jr. recorded the entire vacation with a tape recorder. Kevin Sr. still has the tape in his possession, and has not played it back since until years later.

Cut to the Departure, as Kevin Garvey Sr. began hearing voices minutes after it occurs. The man spent three to four years fighting the voices, winding up in a mental institution until he began listening to them. They told him to go to Australia, and he did. He gets to Australia, and finds himself going on an acid trip for two weeks on something called "God's Tongue". Other than seeing his son through a TV screen leading to "Purgatory", he also sees a chicken named Tony, the only chicken to not be departed in a small town in Australia. Tony pecks at Kevin Sr.'s tape of him and his son from 1981, making Kevin Sr to listen to it right where he left it, in which Kevin Jr tells his father to sing "Itsy Bitsy Spider" to make the rain go away, and it does. Kevin Sr is on a mission, and believes on the 7th anniversary of the Departure, when the flood comes crashing down, he has to sing to make it all stop. Not "Itsy Bitsy Spider" though.

For the past three years, between Seasons 2 and 3, Kevin Sr. has been following a song-line through the Australia outback, learning many religious songs and religious speakings in preparation for the 7th anniversary. Since then, he has talked with Matt Jamison via phone about his travels, only to receive a copy of Matt's book about his son, and not about him. Take note, this occurs a couple weeks before the main events of episode 1 this season, considering Mary and Noah are still with Matt at this point. Calling Matt's book nothing but lies, Kevin Sr throws it in the trash, except one page that becomes VERY significant later. He reaches his final destination: Christopher Sunday, the only person who knows of the song Kevin Sr needs. Through an accident, Kevin Sr falls off of Chris's roof and lands on Chris, breaking his own foot, and fatally killing Chris.

With the songline now incomplete, Kevin Sr wanders around the Australian outback with crutches, coming across a man who burns himself alive, accidentally ruins the tape of him and his son in the rain, and winds up getting bitten by a poisonous snake. He manages to reach a cross, and begins to pass out/die from his snake bite when he awakes in a bed THREE WEEKS LATER, with an IV in his arm, and a catheter on him, under the care of a group of people who are building a church and an ark. He calls Matt up, who at this point was left by Mary and Noah a week or two prior, and Matt asks for a copy of the copy he gave Kevin Sr, because Kevin Jr has it now. After telling Matt he destroyed his book of lies, Matt tells Kevin Sr to go fuck himself. Later that night, Kevin Sr awakes to see the women of the group drowning the Australian police officer Kevin, and is knocked out by them with a dart.

Now we're caught up to where the previous episode left off, and we figure out what the hell was going on. And now, we must follow the story of Grace, the woman leading the group of women in the previous episode.

Grace and her husband David had adopted 5 (or 6) children in their lifetime and were a very Christian loving family. On the day of the Departure, while away from home, Grace witnessed a woman vanish before her eyes. Grace returned home, with no signs of her children or husband anywhere. Believing she has served right by God and granted her family access to be on his side, Grace felt accomplished with her life. That is, until two years later, when it was discovered her children had not Departed. The children had witnessed their father vanish before them, and then set out on foot in the desert in search of their mom. They got lost, and died in the hot outback sun, where their remains had not been found until two years later. Feeling guilty about the loss of her children, Grace built the cross on the spot her children died, and everyday rides her horse up there to make sure no one suffers the fate her children did. That is how she came across Kevin Sr, near death from a snake bite, and among his belongings, a page from a book that read like Scripture. The page reads about a police officer named Kevin who died and returned amongst the living. Believing Kevin Sr to be a messenger of God, and the page being the message, she gathers her friends and spends three weeks building the church and ark in honor of the passage. With a police officer named Kevin living 12 miles from her house, she and her lady friends seize the man, and believing him to challenge them, drown him so they could prove themselves to him. Kevin Sr tells her she got the wrong Kevin.