Donatello told me that after Nathaniel had run off, he slipped on mud and fell, but rejected Donatello's help and kept running away from him. Donatello called out to him to stop and that made Nathaniel turn around and yell at Donatello. He said that he was lucky that he never had to deal with the stress that comes with everyone expecting him to be perfect and rule the "right" way, when everyone has a different version of ruling "right."
Donatello tells him that everyone is stressed in their own way and that's the reason why we are supposed to be polite. We never know what's going on with the other person, so we should always be kind. Donatello convinced him to return to camp with him, but as Nathaniel made his way to him, the ground began to slip and grumble. It was a landslide, and it was headed straight for Nathaniel.
Donatello grabbed him and they got to a cave before they could be buried alive, but they were sealed in. To make matters worse, Nathaniel was burning up with a fever. Donatello told me how he picked him up and tied him to his back using his shirt and tried to find a way out. When he was about to give up, a blue sphere appeared in front of him and led him to a small crevice above him.
Donatello followed the light, but it disappeared once he got to the opening. He heard a few voices calling out to him and Nathaniel, as he was trying to climb out through the crevice. However, when he was almost out, his foot slipped on a wet rock.