"Know This, We've Noticed" is the first episode of the ninth and final season of One Tree Hill and the 175th produced in the series. It was broadcast on January 11, 2012. As Brooke and Julian begin to adjust to life with their new children, Haley and Nathan find themselves dealing with similar issues. Although they don't know it yet, faces from the past threaten to interrupt plans for all their futures. Meanwhile, a mysterious problem arises for Clay and Quinn.