In the year 1859, Nathaniel Essex is living with his wife on the outskirts of London. He has a great passion, curiosity, and fascination for Darwin’s work

Nathaniel presents a lecture to the Royal Society where he discusses his theories of genetic mutation. He speaks of ‘parcels of hereditary information’, which, when combined in the children of genetically superior individuals, will mutate. He wishes to call the parcels Essex factors and are of course the X-gene

Nathaniel is ridiculed and has a drink later. He meets a man who shows him circus freaks and wonders if they’re actually mutants. Later he recruits the man and his friends to join his cause of scientific experimentation- the men that join him become the Marauders

After a 400 year hibernation after defeating Vlad the Impaler, Apocalypse awakens in Victorian England. The Marauders stumble upon his hibernation chamber and plan to give him to Essex of which Apocalypse is curious as to why he wants him

He demonstrates his power by telekinetically ripping out the skeleton of a Marauder

Elsewhere, Jean and Cyclops are time-displaced again to England in different locations of the city- Jean in a church, Cyclops in the sewers

Nathaniel’s wife Rebecca is curious about the work her husband performs in his Annex. What she sees horrifies her which is the body of their deceased son in a tank. She runs to the grave and digs up his coffin to find no body. She faints in horror. Essex sees this and tries to rationalize at which point Apocalypse appears and offers an alliance

A personage from the Askani sisterhood appears to Jean and tells her she brought her to this time to find Essex and somehow stop Apocalypse. She has exactly 2 days to do this or the future is in jeopardy

Rebecca and Nathaniel argue over what just transpired between them. She asks him to cease his abhorrent work of which he hesitates and she realizes where his heart truly is

Jean travels to the Essex estate to look for Nathaniel and meets Rebecca

On a tip from Rebecca, and from Cyclops’ side a Marauder, they both head to the Hellfire Club where Apocalypse revealed himself to the people

Jean and Cyclops realize Nathaniel Essex is Mr. Sinister

Apocalypse beats Cyclops and offers him to Essex to dissect. He offers him a place by his side and Essex contemplates about having longevity to study enhanced beings forever

Essex helps Jean up after being defeated by Apocalypse as well. She persuades him to go back to Rebecca at Essex house. His circus freaks are running about, freed, by Jean and Rebecca when they met

Essex arrives at Rebecca’s deathbed, dying in child labour of which the baby died from premature birth. He seeks forgiveness but she says that she cannot give it to him and that he has become sinister

Jean rescues Scott from the location he was held in by Apocalypse (hibernation chamber) where he was forcibly being infected by the T.O virus. 

Essex arrives ready to give himself up to Apocalypse after losing everything he loved. Essex enters a machine and the transformation begins. Cyclops and Jean watch

After an introspective conversation with Sinister, he points them towards Buckingham Palace where Apocalypse plans to kill the Queen. They stop him and divert a war, shifting the timestream and making Sinister obsessed with the Summers bloodline. Revealed that Sinister released a plague onto Apocalypse weakening him thus allowing for his defeat

Apocalypse figures out Sinister’s ploy to kill him and tolerates it seeing it as a sign of strength. He spares Sinister but Sinister realizes he is at the mercy of Apocalypse and may have to eradicate the mutant species if they are unfit to exist in the Age of Apocalypse which is in direct contrast to Sinister’s scientific aim to study the mutant gene

The Askani sisterhood personage (Sanctity) reappears and takes the Summers’ through time explaining that Sinister needed to exist so that Cable would (Sinister created Jean’s clone Madelyne Pryor who conceived Cable with Cyclops)

23 years later in 1882, Darwin passes and Sinister pays his respects. He then completely forsakes his former life