UNIT: Incursions: The Power of River Song Part 1 (excerpt)

UNIT has been assigned to monitor the switch-on of a revolutionary new power system - they know from experience such things can be tricky.

Nearby, Osgood and Lieutenant Bishop investigate mysterious disappearances - and appearances of trans-temporal phenomena. Kate would like to ask the Director some questions, but she's proving strangely elusive... until there's a murder.