The fourth series in the “Torchwood” franchise continues the story of a crack team of charismatic agents who gather intelligence and protect humanity from alien threats. Led by their mysterious captain, Jack Harkness, members of the Torchwood Institute act outside the jurisdiction of the government, the police and the United Nations, an independence that may prove fatal when they’re faced with their fiercest threat to date. It begins with a day when nobody dies, and soon death itself ceases to exist. The result is a population spike, and with it comes worries that resources will eventually run out and society will collapse. Living forever is not a natural occurrence, so who is behind this global conspiracy? The Torchwood team — and a CIA agent named Rex Matheson — search for the truth.