When keeper Zac Halsey's corpse was found in the tiger enclosure at Harefield Zoo in 2006, the assumption was that he had been mauled to death, but blood found during the refurbishment of his flat now suggests that he was murdered and his body dumped in the compound. He had recently been to Spain where the knife that killed him was purchased. An animal rights campaigner, sacked security guard and a couple with whom Zac enjoyed extreme sports, are all suspects and all seemed to have been in the zoo the night Zac died. Jack works out the killer's identity even though it means he and the team miss his presentation for bravery as a result.