Clancy Crew is Ruby Redfort's best friend. Although he is not an agent of Spectrum and is not allowed know anything about Ruby's work there, Ruby tells him all about it, since he can be trusted very well to keep a secret. Originally, Ruby tried to keep it secret from him altogether, but Clancy was very persistent and knew something was going on, and Ruby had to give in. He is good at deciphering codes just like Ruby and he makes origami with codes written inside for Ruby.
He is shown to be extremely loyal to his friends, especially Ruby, and according to Ruby, wouldn't tell a secret even if you dangled him over a crocodile's mouth. He can't stand ratting on others, even his own sisters. In the third book Clancy is mentioned to have often been arguing with the philosophy teacher, Mr Piper about the concept of good and bad, with Clancy believing that some people only have a good side to their heart and Mr Piper believing that man will always have a good and a bad side. According to the second book, Clancy is afraid of water, despite the fact that he knows quite a lot on the subject. One of Clancy's habits is that whenever he gets worried he flaps his arms. He is bad at French and often has to resort back to Ruby for help to do his homework and assignments for French.
Although Clancy may be portrayed in the book as a character who is easily flustered and scared, he is a great and loyal friend to Ruby who is there for her most of the time when she needs help. He has even managed to help save her life a few times and help solve the mystery. In the fifth book when Ruby was framed and accused of causing trouble at school, even when there was a fake video to 'prove' that it was Ruby who was causing the trouble, Clancy always knew that it couldn't have been Ruby and that if she says it's not true, it's not true. He then manages to prove Ruby's innocence, thus proving his loyalty to her.