Spoiler for Heros if I am right.

[bjornwilde]

the climatic events that led to the dark future Hiro was trying to change and what causes Peter to go 'splodie'.

1-Sylar gets the Illusion Girl's powers or some for of shapeshifting.
2-Hiro, Peter and everyone are fighting with Sylar.
3-Hiro at some point thinks Sylar has changed to look like Peter.
4-Hiro attacked who he thinks is Sylar looking like Peter with the sword, like say across the face.
5-Unfortunately it is Peter and not Sylar, and Peter having absorbed the Nuclear Fellow's powers loses control of them because he is freaked out.
6-Boom.

Sorry I'll go back to not knowing anything about how plots work now.

Okay maybe it's a bit obvious.