Thomas realizes that the only way to save Alby is by making a run for it himself in hopes of to distracting the Griever. He starts Tarzan-ing across the wall, using the vines to move horizontally as well as vertically across the wall face.
Even though it works at first, the Griever closes in fast and Thomas is forced to Spartan-kick the thing away from him. This allows him to make it to the bottom of the wall and hit the ground running.
Unfortunately, after a few minutes of sprinting though the maze Thomas takes a corner and sees three more Grievers sitting there waiting for him. He's trapped.