Roger Shears, ex-husband of Mrs. Shears, is an early symbol of Christopher's investigation. Christopher labels him as the "Prime Suspect" in Wellington's murder after determining that whoever killed the dog must have wanted to hurt Mrs. Shears. Mr. Shears is the only one that Christopher can think of who fits that description, and his character therefore propels both the investigation and the story forward. 

Mr. Shears is also a symbol of deception. Before the events of the novel, he cheated on his wife and had an affair with Christopher's mother. He represents an unknown in Christopher's world, where sense and logic are of utmost importance. Christopher reflects, "And I don't know why Mr. Shears left Mrs. Shears because nobody told me." Christopher then discovers that his father has been lying to him and his mother is alive and living with Mr. Shears in London, furthering Mr. Shears' connection with dishonesty and deceit.

When we first encounter Mr. Shears in London, he has just made a joke at Judy Boone's expense, embarrassing her and subsequently minimizing her feelings. This is our earliest indicator that Mr. Shears is a bully who wholly lacks empathy. When Christopher shows up out of the blue, Mr. Shears exhibits no signs of concern and instead makes sarcastic comments about Christopher's father. He later gets into an aggressive shouting match with Ed Boone and callously tells Christopher that he can only stay for a few days due to the size of their flat. He is also a belligerent drunk who demands of Christopher, "Don't you ever, ever think about other people for one second, eh? Well, I bet you're really pleased with yourself now, aren't you." His actions throughout the final section of the novel make it unsurprising that Christopher is afraid of him. In a story filled with complicated, ambiguous characters, Mr. Shears truly has no redeeming traits.