NBC’s One Chicago is airing its first crossover in five years tonight. Here’s how to watch the epic event featuring "Chicago Fire," 'Chicago Med," and "Chicago P.D.."

The One Chicago universe pulled off the unthinkable: integrating over 20 characters into one thrilling and coherent storyline. In a three-hour event involving Chicago PD, Fire, and Med, the writers achieved a resounding success with the crossover on NBC,

The first One Chicago crossover in five years provided fans with plenty of non-stop action, heart-stopping moments and some fun (but strange) pairings between characters we'd never really seen interact all that much.