Ellis is a worker at Paddock 11, where the Indominus rex is kept. When the control room registers no thermal signature, it seems as though the dinosaur isn't in the enclosure anymore and has escaped, and so Ellis accompanies paddock supervisor Nick and Jurassic World's chief animal trainer Owen Grady into the paddock to try and discover how Indominus managed to scale the humongous wall.
In the control room, Indominus' tracking implant is activated, revealing she is still inside the paddock. After learning of this via Nick's walkie-talkie, the three men immediately bolt for the front entrance. Nick sees Indominus through the trees in that direction and runs the other way, but Ellis and Owen don't and keep unknowingly running straight towards danger.
Nick doesn't even get a chance to shout a warning. Only when Indominus actually steps into view between them and the front door do the two realize their error.
Wisely, they turn and start running for the back door (which is where Nick went).
Ellis, stumbling because he keeps looking back over his shoulder, is snatched up in the dinosaur's enormous hands.
Although this happens out of view of those in the control room, they do get to hear his screams of terror and the crunching sounds as he gets eaten.