Thieves in the Night

It seems too farfetched even for an airport novel. Three men breeze into a heavily fortified police station, stroll straight to the office that contains its most sensitive information, and walk out again with highly classified documents. But that's just what happened last week at Castlereagh Police Station in Belfast. The perpetrators of this audacious crime did more than just provide the authors of cheap fiction with a new plot twist — they managed to spook the real-life spooks.

Castlereagh was supposed to be secure. The small complex of squat brick buildings in east Belfast houses the divisional headquarters of...