This article contains spoilers for the DC Cybernetic Summer one-shot.
Batman's worst mistake is back. The Dark Knight may be a key member of the Justice League, but he hasn't had much of a reputation for playing well with others. He's spent an inordinate amount of time studying his friends, identifying their weaknesses, and preparing strategies to beat them in the eventuality they turn back. Of course, this tends to backfire quite badly, because those plans tend to go amiss.
One of Batman's worst mistakes was the construction of Brother Eye. Batman used his wealth as Bruce Wayne to construct a massive satellite in space, designed to conduct clandestine surveillance on the entire planet. He decided on these extreme measures when he learned one of his allies, Zatanna, was violating his friends' privacy; Batman was blind to the irony of responding by doing far worse. Unfortunately Brother Eye went wrong under the baleful influence of Maxwell Lord, developing cybernetic troops called the OMACs - the One Man Army Corps - to take down superheroes. OMACs even successfully defeated the likes of Superman and Green Lantern. In the end, Brother Eye was destroyed - or so Batman believed.
In this week's Cybernetic Summer, Batman learns Brother Eye survived the destruction of its satellite. Ever attentive, he notices disused satellites in space dropping out of fixed orbits, fusing on to an old Bulgarian space station. Batman immediately suspects that this is Brother Eye, and heads into space to investigate - without backup. As far as Batman is concerned, this was his mistake, and it's his responsibility to correct it. When he infiltrates the Bulgarian satellite, Batman learns Brother Eye survived by dispersing parts of its consciousness into the space junk. It has been bringing its different parts back together, restoring itself in order to continue its mission - the destruction of all superhumans on Earth.
The threat is phenomenal one, because if it successfully reintegrates its central consciousness, it will be able to hack into every piece of technology on the planet. Every smart phone or GPS transmitter can be used to track a hero, and anything can turn into a weapon under Brother Eye's control. Imagine a SatNav encouraging a driver to speed down a road, unaware the bridge at the other end is undergoing repairs; or planes crashing from the skies because superheroes and vigilantes happen to be on board. What's more, because Batman was foolish enough to head into space without backup - even Alfred isn't on call - nobody else knows what's happening.
Naturally, Batman deals with the immediate threat. Unfortunately, even though he destroys the satellites, Brother Eye's consciousness is able to escape once again - and he has absolutely no idea where it has gone. Batman's worst mistake is back - and every superhuman in the world is in danger as a result.