Visiting Gallifrey to attend an academic conference, the Sixth Doctor's old friend and mentor, Duotheros, requests that he use the TARDIS to examine a temporal anomaly centred on Bixor. The planet, once thriving, appears to have mysteriously eradicated itself, substantially reducing the number of people interested in buying Duotheros' definitive history of that sector of space. Will the Doctor's investigations reveal the cause? Or does Bixor's untimely demise have something to do with a certain blue box?