Francisella tularensis is the bacterium that causes tularemia, a life-threatening disease spread to humans via contact with an infected animal or through mosquito, tick or deer fly bites. Scientists have unraveled the process by which the bacteria cause disease, finding that F. tularensis tricks host cell mitochondria, which produce energy for the cell, in two different phases of infection. These basic science findings could play a role in developing effective treatment strategies.