Continuing this week is the fourth season of the hit drama series following a team of special agents who investigate Navy and Marine Corps-related crimes. In this episode, a nuclear power plant inspector reports that he has been poisoned with a lethal dose of radiation. As the team tries to identify those responsible, Ziva’s composure is rattled when she develops feelings for the dying man.

Gibbs and the team are confronted with an extraordinary case when Lieutenant Roy Sanders walks into NCIS headquarters and says, “I need you to investigate a murder... mine.” It transpires that Sanders, an inspector for the International Atomic Energy Agency (IAEA), has been infected with a deadly dose of radiation. He has just returned from a trip to inspect a nuclear power plant in Brazil, but neither of the colleagues that accompanied him, Mark Sadowski (Mark Vann, ‘CSI’) and Diane Russio, has reported feeling ill. Only Sanders is contaminated – and this may be because his personal radiation-detector badge was sabotaged.

An examination of the badge reveals that it was indeed faulty, and failed to alert Sanders to the presence of radiation. But the team can find no evidence of foul play, until Ducky identifies the type of radiation in Sanders’s body. This particular isotope is “colourless, odourless, tasteless and soluble in water” – making it the perfect poison. While the ailing Sanders is transferred to a special hospital, Tony and McGee retrace his movements to determine where he was infected, and pinpoint the location to a shooting range that the lieutenant visited with his boss, Sadowski.

Meanwhile, the doctor reports that Sanders’s level of radiation has increased since he entered the hospital, which means that someone is still poisoning him. The agents suspect that Sadowski could be to blame, as he was present at both the hospital and the shooting range. However, Sanders’s boss insists he is innocent – and Ducky is able to support his claim.

The pathologist tells Gibbs he has established how the lethal radiation entered Sanders’s body. “We’ve found the smoking gun – with the emphasis on the smoking,” he says. It would appear that the cigars that Sanders was fond of smoking were laced with the deadly isotope. The hapless lieutenant continued to smoke a few sneaky cigars in the hospital – little realising that he was poisoning himself further. The revelation clears Sadowski of blame because CCTV footage from the shooting range shows him breathing in the same smoke. This would mean that Sadowski is also infected – and in due course, he too collapses with radiation sickness and is rushed to hospital.

Gibbs now knows how the lieutenant was poisoned, but he is no closer to identifying the culprit. He turns his attention to Sanders’s job as an inspector of foreign power plants. The lieutenant’s next mission was to carry out surprise inspections of nuclear facilities in Russia, Pakistan and Uzbekistan. Could it be that one of these countries got wind of their imminent visit and decided to derail it by poisoning the inspector?

As Gibbs gets closer to solving the riddle of Sanders’s poisoning, Ziva finds herself facing uncomfortable new feelings for the lieutenant. At first she is puzzled by the sense that she has met Sanders before. “I feel like I know him,” she says. She soon realises that she sees Sanders every day on his jog through Washington DC, and happened to remember his face. As she keeps him company in his hospital room, Ziva warms to his affable nature – something that even Tony notices. “Are you falling in love with a dying man?” he asks. “The look on your face says you are.” The normally reserved Ziva does not know what to make of her feelings, especially as Sanders seems doomed to meet a tragic end...

Friday March 21 at 9pm on five