The story will involve Thanos attacking Earth while the Avengers are in space uniting the universe against the Builders. The event will crossover with Hickman's Avengers and New Avengers books, with two different perspectives being told in each book. Avengers will follow the Avengers while they are in space recruiting various alien races to fight against the Builders with Nova and the Guardians of the Galaxy, while New Avengers will detail Thanos' attack on Earth and the heroes left behind to deal with him.
Marvel has even released a animated trailer for the event
The first issue is available August 14th with Iron Man and the Illuminati staying on earth to maintain a home front while the Earths Mightiest Heroes take to space to go head to head with the Builders.
The Builders are a race from the Beginning of time who have come to destroy Earth.
Here are a few preview pictures of Infinity#1