Sterling is a city in the state of Colorado.
Kidnapping of Franklin Hall
S.H.I.E.L.D. decided to move one of his most prominent scientists, Franklin Hall, to a secure facility in an undercover but heavily guarded track, masquerading as a common supply delivery. Hall decided to leak the information regarding his route in order to be discovered by Ian Quinn, Hall's former colleague, so that Hall could approach Quinn's cluster of Gravitonium and destroy it. Under Quinn's orders, a section of the road near Sterling was seeded by Gravity Field Generators, in order to easily get rid of the vehicles that formed the convoy transporting Hall.
The transport went as usual, being Agent Mack the driver of the truck and having at least two vehicles escorting him. However, one of the vehicles suddenly was quickly lifted to the air, falling right in front of the truck, and Mack was forced to evade it, almost losing control of the truck.
Mack activated the truck's computers to calculate safe alternative routes, choosing the alternative route two, and informed the S.H.I.E.L.D. CT of the attack; however, he couldn't identify the attacker, and the truck was lifted just like the previous cars before it.
A group of men hired by Quinn arrived, using heavy construction equipment to dismantle the truck, and retrieved Hall, who was taken to Malta to meet Quinn in a country outside of S.H.I.E.L.D.'s jurisdiction.
Search of Franklin Hall
The team arrived at Sterling, explaining to the newest recruit, Skye, the importance of a red-classified asset like Hall, and how the security should have been heavy, but seeing one of the SUVs that escorted Hall hanging on a tree made them think that something dangerous had attacked them.
Coulson and Melinda May interrogated Agent Mack, the truck driver, who told them that no attacker was seen in front, behind or above them, but what really worried him is that the attacker knew their route, insinuating that someone inside S.H.I.E.L.D. was working with the attacker.
Simmons discovered a gravitational anomaly in a specific place, having activated one of the Gravity Field Generators with the Electro-Static Field Scanner she was using. Once Fitz was able to deactivate it, Simmons retrieved the Generator and handed it to Coulson.