Robert Neville is the sole survived of a deadly disease that turns humans into ravenous vampire like creatures. He has to search for a cure, and fortify his house before night or the undead will kill him.
A major theme is loneliness:
Robert‘s wife and daughter have both succumbed to the disease, so it‘s late nights of booze for him. Not to mention the only other people that are left are the lifeless vampires who are a sad reminder of the past.