The Tesseract

The Tesseract or Cosmic Cube is an enchanted object of unparalleled power that was once owned by Thor and Loki's adopted father Odin

The Tesseract, is one of the most powerful artifacts in the universe. According to Fury, it holds great power that is almost unlimited. Black Widow states that it has enough power to destroy the entire planet.

The Tesseract has the capability to open rifts through space and time. While it was thought to be taken back by Thor it was really stolen by Laufey under Sigma's orders. However S.H.E.I.L.D  got the Avengers on the case and they took it back. Realizing the danger it could be placed in, Fury's superiors took it for themselves thinking Fury was foolish for giving to Thor.

Soon after Obodiah Stane learns of the Tesseract and after Discord escapes, Stane tells Discord about the cosmic cube. Discord intrigged by this, he makes a plan to steal the Tesseract with Obodiah Stane and decide to go with one of their allies to make an attack on S.H.E.I.L.D. The attack was sucessfull hurting everyone but Fury and Coulson.

Spoilers alert

Agent Coulson and Nick Fury meet up with Soul Eater Evans, Lizbeth and Maka Alburn and tell them about the attack and the Tesseract. The three decide to help them get it back and stop the ones behind it.