The Bells of Saint John

London, 2013. "Danger. This is a warning. A warning to the whole world. You're looking for Wi-Fi. Sometimes you see something, a bit like this. Don't click it. Do not click it. Once you've clicked it, they're in your computer. They can see you. If they can see you, they might choose you. And if they do... you die."

When Clara Oswald has problems with her Internet, she's given a telephone number: the number of the "best help line in the universe". When the Eleventh Doctor answers at the other end, Clara is pulled into a life of adventure and mystery. But danger is lurking in the signals, picking off minds and imprisoning them. "It's like immortality, only fatal." But can the Doctor save Clara before... "I don't know where I am!"