The title of issue #1 is "The Domino Effect". That term refers to a chain of causality, as when a line of dominoes fall, with each one setting off the next one. That is how this story has been structured: Pyg's work turns an ordinary girl into Red Hood's sidekick. Red Hood's remark sends Dick to the UK where he accidentally resurrects an evil Batman clone. That clone goes to Gotham where his attack on Damian is likely to help lead to Damian battling Dick in the fourth arc. And if Doctor Hurt / El Penitente attacks Batman while Robin is already occupying his attention, the attack might succeed, resulting in the kinds of things we saw in Batman #666 -- an anguished Damian as Robin kneeling over the bloody Batman. Which might even lead to Damian selling his soul to the Devil to make up for the loss of Batman. Which would fulfill what El Penitente said in #6 (and Morrison said in interviews), that by beating Dick Grayson and Damian, Doctor Hurt would have thereby settled his score with Bruce Wayne.
That is likely the sense of "domino" intended outside the story, by the writer. But that leaves the explanation of what's going on inside the story, which still has some blanks to fill. Here's where it gets interesting, and interactive: The rest of the story, broken down into multiple choice.
1) What is Oberon Sexton's secret?
1A) He is really Mangrove Pierce
1B) He is really the Joker
1C) He is the last life that Bruce Wayne is living in the Omega Sanction
1D) He is Grant Morrison, who is writing the same story that he's in
1E) He has some superhuman ability
2) What is the Joker's role in this story?
2A) He is Oberon Sexton
2B) He is the killer of Cardinal Maggi whom Sexton is tracking
2C) He lent his circus from The Killing Joke to Professor Pyg
2D) Nothing we've seen yet; he'll arrive later
3) What is Bruce Wayne's role in this story so far?
3A) He is the soul inside Oberon Sexton
3B) He has arranged the appearance of the dominoes through actions from his past lives to communicate something to Dick Grayson
3C) He has not played a direct role
4) Is Toad actually dead?
5) Was the antidote Dick found real, or a trick?
5A) Really an antidote to the contagious addiction
5B) "Meant to be found", and to trick him
6) Who was the recipient in the drug deal before #1?
6A) A representative of or friendly partner of El Penitente
6B) Someone who wants to work against El Penitente
6C) It doesn't matter
7) Why did Pyg says that Niko betrayed him?
7A) The entire deal run by Toad was not authorized by Pyg
7B) He expected cash, not dominoes
7C) Because Toad, Niko, and Lev failed by being captured
7D) No reason; he's crazy
8) What is the physical nature of the dominoes?
8A) They are totally ordinary dominoes
8B) They can spread the contagious addiction
8C) They have a regenerative healing power for those who hold them
8D) They are something horrifying, such as human bone
9) Why are the single dominoes showing up?
9A) They are a calling card, brag, or a taunt, counting down to something bad
9B) They are going to spread the contagious infection
9C) They were talismans or instruments of healing for El Penitente's underlings
9D) Bruce Wayne is trying to tell Dick something
9E) They are symbols in a story by Oberon Sexton / Grant Morrison
10) How were the dominoes delivered?
10A) A metahuman snuck in with speed or invisibility, or teleported them
10B) Damian did it
10C) Multiple agents on-scene, like Tony Li, did it
10D) The writer, Grant Morrison, made them appear
10E) The people with dominoes had them the whole time
11) Given the planted dominoes, why did Pearly also have dominoes?
11A) No reason; coincidence
11B) Someone is spreading dominoes far and wide
11C) Someone made a point of planting them to confuse Dick into thinking they are part of the sequence, but they are not
12) Why is the secret of the dominoes "terrifying"?
12A) They are counting down to Dick's death
12B) They are counting down to massive numbers of deaths
12C) They are composed of human bone
12D) They are associated with the deaths of the Waynes or Graysons
I'm not even asking who the Domino Killer is! That's implicit in the answers to the other questions.
13) What did El Penitente ask of Oberon Sexton?
13A) To offer the results of his investigation to El Penitente
13B) To play a part in an upcoming attack on Dick
13C) To rewrite the story and thus plant Pearly's dominoes as a false clue in front of Dick
13D) To rewrite the story in a way that will attack Dick in an overwhelming fashion
14) Are the financial irregularities at Wayne Enterprises related to the main plot?
14A) It's a totally separate plot
14B) It's part of an attack by El Penitente
14C) It's part of an attack by Talia
14D) It's part of an attack by the Joker
15) How will the fourth arc tie into Batman #666?
15A) Dick will be the Batman who dies; Damian will deal with the Devil to bring him back or defend Gotham
15B) The clone will be the Batman who dies; Damian, not realizing that it's a clone, will deal with the Devil
15C) No Batman dies; Damian will deal with the Devil to save Gotham
15D) Damian doesn't actually deal with the Devil, but meets him
16) How will the fourth arc tie into Detective #235?
16A) We'll finally find out about the Waynes' involvement with the Black Glove
16B) Not at all
16C) We'll see some scenes that speak to this, but they will be ambiguous
I think it's safe to say that the answers to most of these questions would wrap up just about any remaining mystery. Now -- what are the answers? There were some very leading questions among the bunch. I don't think I see the whole picture yet, but I think many of the questions can be narrowed down to a much smaller range of possibilities than the full set I listed. Yet, there may be some correct answers I didn't list. I invite people to give their answers. I'll offer mine early next week. Of course, there'll be opportunities to revisit the questions after every remaining installment of the story.