As the boilerplate introduction to the Supporting Cast line states, superheroes are surrounded by lots of "ordinary people." The Supporting Cast line aims to present NPCs that GMs can drop into just about any Mutants & Masterminds campaign, and Precinct 21 certainly fits that bill. The product gives you full write-ups on three cops and one PI, plus a super-dog on the K9 squad and a super-villain tied to one of the several plot hooks provided. For the most part, this little sourcebook is setting-neutral, and the author has taken care to give good advice about integrating Precinct 21 into the GM's own campaign. However, there are a few "gaffes" in this regard; for example, using officer Jeff Romero as written also requires your campaign to have a superhero called "Kid Orion." This is a minor complaint, though, and easily adjusted by even a novice GM. I definitely think this product is well worth the price.