"Blue Bloods" is at its best when it showcases good, old-fashioned police work. The Reagans all have their roles to fill within New York's echelon of justice, from Frank Reagan (Tom Selleck) being the police commissioner to Erin (Bridget Moynahan) taking on the role of assistant district attorney. In any given episode, they'll have various cases they're working on, occasionally intersecting as the writers see fit to have them bounce ideas off one another or find evidence to help them in their own respective cases. Occasionally, this requires them to get a bit creative, as they come up against one obstacle after the next to finally catch their perp.
There are countless examples throughout the series where audiences get to see the Reagans put their feet on the pavement and get to work, making the streets a little safer. And there's one such example in Season 2 that exemplifies the entire Reagan ethos.
In Season 2's "No Questions Asked," the storyline opens with a robbery. Later, a gun buyback program took place where people could turn in their firearms under the policy of "no questions asked." When an officer recognizes a gun as being part of said robbery, she takes it to Danny (Donnie Wahlberg) and Jackie (Jennifer Esposito). They become irate with her when she took evidence from the gun buyback to them. However, now that they have a solid lead on one of the criminals, they decide to pursue other avenues to catch the perp by the books.
It ultimately leads to the criminal's arrest by the end of the episode, with Danny and Jackie tracing him back to his apartment, where a foot chase ensues, which tends to be the case with many of Danny's arrests. But he manages to catch his guy.
It's a fantastic arrest because it shows just how proficient Danny and Jackie are at their jobs. The case may have started in an inopportune place, but they managed to reverse-engineer the situation to where they could put the perp behind bars properly with evidence they could actually use in a court of law.