The Bill: Time Bomb

When a letter bomb is delivered to the offices of a high profile company, the manager believes it to be a hoax. But Grace is concerned that it is the beginning of something sinister. Initially the officers suspect that a regular courier is behind it - the man had been thrown out of the building a few days previously for harassing a PA. Then the investigation takes a shocking turn when Callum discovers bomb-making equipment at the home of the manager's brother.