Complex sentence: Of all the Yarders, Gregson comes the closest to meeting Sherlock Holmes on intellectual grounds while acknowledging Holmes's abilities, even admitting to Holmes once that he always feels more confident when he has Holmes's aid in a case.
Split into simpler sentences: Of all the Yarders, Gregson comes the closest to meeting Sherlock Holmes on intellectual grounds, while acknowledging Holmes's abilities. He even admits to Holmes that he always feels more confident when he has Holmes's aid in a case.