Close to retirement, he secretly breaks chain of command and puts his resources into "Hamsterdam," three zones within his district where drug dealers are pressured to non-violently congregate in exchange for informal legal sanction.

Colvin's philosophy of policing involves protecting the community he serves by making quality arrests through the use of trusted informants on his foot post.

Toward the end of his career, he begins seeing the War on Drugs as an ineffective waste of time and resources that has led to many needless casualties in his district.

All of Baltimore's district majors are under extreme pressure to reduce the city's violent crime rate from Mayor Clarence Royce, who is seeking re-election.

After the attempted murder of Kenneth Dozerman, Colvin decides that he will independently set up three "free zones" in the Western where addicts and dealers can conduct their business under supervision, but without interference.

Colvin does not seek the permission or approval of his superiors before implementing his plan, and ignores the concerns of his subordinates, including Mello and Ellis Carver, who are charged with ensuring no violence takes place within the free zones.

After implementing the Hamsterdam plan for five weeks, Colvin delivers a cumulative 14% reduction in the felony rate, unheard of in the Western's history.

However, in the meantime, Herc leaks information about Hamsterdam to the press after rejecting Carver's request to help him move a homicide victim off the free zone premises.

After realizing that public opinion is sharply against the free zones, and that there are broader political ramifications (the White House's Deputy Drug Czar threatens to pull all Federal funding from the city if the entire endeavor isn't immediately ended and publicly negated), Royce recants and decides to end the Hamsterdam experiment.

Colvin has a major impact on Carver, convincing him to reassess his role as DEU sergeant and to take a more community-minded approach to policing.

Colvin has developed a reputation among academics as a result of his Hamsterdam experiment, and the Deacon helps him secure a job offer with Parenti as a field researcher.

Together, they isolate ten corner kids into a classroom where Parenti and a UM doctoral student study them while Colvin acts as the mediator.