The journey to finding out what that flashback was all about begins in the present, with Reed Strucker.
This is complicated a bit by the fact that Reed hasnt seen Otto in decades.
Andy and Lauren have never even met him, even though hes alive and well in upstate New York.

Credit: Eliza Morse/FOX
Caitlin calls him a difficult man.
With Sentinel Services in overdrive, now even church sanctuaries are being raided for mutants.
And thank God even more that the Underground fighters have gotten so damn good at combining their powers.
Although the speedster seems unbeatable at first, Marcos soon traps her between two sunbeams.
Thats not even the only call-out that the Grant Morrison era of X-Men gets in this episode.
Later, when interrogating the speedster, Marcos realizes shes acting like an addict.
The power-enhancing mutant drug Kick, first created by Morrison, is apparently part of the Sentinels brainwashing regimen.
He takes Reed upstairs and shows him some family photos.
Andreas and Andrea Strucker, Otto names his parents.
Otto was horrified by their actions and determined to stop it from ever happening again.
Thats what drove him to Trask, where he tried desperately to find a cure for the X-gene.
That was the source of Reeds childhood sickness.
When Campbell refuses to take no for an answer, Otto lights up his nuclear-level energy powers.
Despite his probably-infrequent use of his powers, Otto is so overwhelming that not even Pulse can contain him.
Reed isnt so lucky; his dad is already dead from gunshot wounds.
Thats quite an emotional roller coaster of a day.
No wonder Reed is so shaken when he gets back to his family after burying his father.
But hes so emotional, he doesnt even see Andy and Lauren holding hands.
Im constantly impressed by all the amazing power combinations this show keeps coming up with.
Mutant powers arent the only thing that runs in the Strucker family.
He believed this was protecting Reed, but was it his choice to make?