Two policemen drive, under your command, a modified Nissan 300ZX Z32, a special high-powered car enforcing the law. After they get a call from Nancy, at the Police HQ, telling them which criminal is about then it's race time. With (limited) turbos on full, they're off in hot pursuit. The chase splits into two section at each stage. First comes the find the criminal, who has a substantial lead, and then when in sight the second part comes in which your siren goes on, a big red arrow indicating the position of the criminal (car) comes in and you've got 60 seconds to ram them off the road. Fortunately this time the boys hold guns (in contrast to the original Chase HQ), and the passenger can rise out of the T-top and shoot at the main criminal until his car blows up. Note that enemy vehicles (bikes, cars etc) are placed throughout the level and will attempt to shoot at or ram your car as you attempt to pursue the main criminal. As you race against the clock, traffic is a major problem too, and incoming vehicles hit you easily resulting decreasing your speed and losing the precious pursuit time. There are power-ups in the form of a helicopter that drops weaponry (i.e. rocket launcher) to you too.
Ok, Chase H.Q. II is fun, but repetitive. The main improvement to the Chase HQ formula is a gun, but added firepower doesn't significantly increase the gameplay quotient.
The Atari ST port features quite fast action, nicely drawn backdrops with enough graphics similarity to the arcades, including waterfalls, unfinished sections of elevated highway etc. Of course scrolling here suffers a bit when compared to the Amiga or the original arcades version, but it's quite playable.
Sound is good, but nothing really special to get excited, including music and SFX during gameplay such as engine throttle, gun fires, sirens and explosions.