The diary entries document Chris McCandless, also known as Alexander Supertramp, as he ventures into the Alaskan wilderness alone to live off the land. In the first entry, he expresses his excitement to reach Alaska and begin his great adventure living independently in nature. In later entries, he discovers an abandoned bus to use as shelter, hunts and kills a moose, but then struggles with hunger as his luck changes. In the final entry, on his 100th day in the wilderness, he has become too weak to leave and realizes he now faces a serious threat of death without medical help.