。
There wasn't a single person around.
Literal
Surroundings [in-には] who-one-person didn't-exist.
誰一人~ない is an emphatic negation — 'not a single person.' The 一人 after 誰 strengthens the negation beyond plain 誰もいない, emphasizing absolute emptiness. には as a composite particle marks the location as the topic of an existential statement.