Mac's decision to take him on is an honor and a responsibility that Danny attempts to live up to each day.

In "The Party's Over," Danny tells Stella that he comes from a family of cops, though the details of this are left unclear.

When Danny protested, Louie called him a disgrace and told him to leave.

The cold case is eventually solved, but Louie is beaten into a coma by the remaining members of the Tanglewood Boys.

Danny is shown explaining that he finally understands Louie's actions.

At the end of the episode, Mac tells Danny that he is on the promotion grid, meaning that his training and experience have prepared him to sit for the next examinations for Detective Second Grade.

He is temporarily removed from the promotion grid (meaning he must wait to be reinstated, and then wait for the next examination schedule) after being accused of shooting an undercover police officer In the subway (episode 121, "On The Job").

On the show, Danny has displayed a tendency to follow his intuition when solving a case, rather than relying on the evidence, for which Mac has criticised him (episode 105, "A Man a Mile").

During the beginning of season 1, Danny is a Detective Third Grade and mainly works in the lab or accompanies Mac or Stella to crime scenes.

Due to Danny's DNA appearing on an old cigarette butt at the crime scene, Mac is forced to temporarily revoke Danny's badge until Danny is proven innocent.

Though hurt, Danny understood why and obliges without complaint.

By the sixth episode, he is given solo control of his first crime scene.

Mac tells Danny and Aiden that the crime scene at a robbery homicide is theirs, and that Danny is the officer in charge.

The show's character work is probably its strongest aspect, with multi-season arcs for several of the characters, particularly Mac, Danny, and Lindsay.