Torchwood is called in to investigate a burglary gone wrong. The targets were a married couple, Mike and Beth, but one of the robbers wound up dead and the other was grievously injured. The Torchwood team soon realises that Beth is more than she appears -- and more than she knows. Her physiognomy is not entirely human, and some of her memories have been locked away, hidden even from Beth herself. Jack deduces that Beth is an alien sleeper agent, acting as a forerunner for a potential invasion of Earth. And, if this is indeed the case, it means that more of her cell is still out there, waiting to be activated.