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An illegal arms racket is discovered after a suspicious container at Tilbury Docks explodes, almost killing Christie. A new elite squad known as Indigo has been formed and Christie is invited to join, leaving Murray frustrated at being passed over.

Siblings Rick and Jenny Foster supply deadly ecstasy tablets in the clubs of Ibiza. The pair are so hard to catch that Indigo suspect there's a mole tipping them off.

A poisonous toad smuggling operation causes a series of deaths to Indigo. An international drugs baron has an old score to settle with team leader Vaughan.

When a teenage girl goes missing, an online pedophile ring are the chief suspects. An explosion kills the main suspect. The team race to find the girl before she is killed.