Of course, I missed this one when it aired originally. I was otherwise occupied that night…
4×11 December 3, 1999
A TIME TO REAP (Serial 48)
Setting: Seattle, WA, UNIT-time
Regular Cast: Hugh Laurie (The Doctor), Sarah Michelle Gellar (Lizzie Thompson)
Guest Starring: Denis Forest (Malcolm), Jonathan Frakes (Agent Blackwood), Paula Devicq (Agent Sarah Hatcher), Peter Mark Richman (Craig Toynbee)
Plot: While leaving his office for the night, a reporter for the Seattle Post-Intelligencer is cornered by a Morthrai agent and interrogated about a recent article on the reclusive scientist Craig Toynbee. The reporter is turned by the Morthrai when he won’t reveal the location of the professor’s lab. At UNIT, Agent Blackwood thinks recent thefts of high-tech equipment might be related to the Morthrai, but the Doctor isn’t interested. The Doctor reads the article about Toynbee and becomes concerned when he learns that a human scientist is experimenting in time travel. Agent Blackwood suggests that the Doctor could help him complete his experiments safely and agrees to set up a meeting, hopeful that the Doctor will finally share Time Lord technology. Toynbee is initially suspicious of the Doctor, but opens up with the Doctor displays his profound knowledge of time. Studying the professor’s work, he confides to Lizzie that while Toynbee is advanced for his time, he is not close to making any key breakthrough. Losing interest, he returns to UNIT, thus failing to discover that Toynbee has been approached by the Morthrai, who have presented themselves as friendly aliens hoping to guide humanity toward “enlightenment”. Blackwood thinks that the Doctor’s interest in Toynbee was just about hoping to find a way off Earth, and tries to convince the Doctor to reveal some of his Time Lord secrets. As soon as Blackwood leaves, a time distortion occurs causing the argument to repeat. Only the Doctor, Lizzie, and Agent Hatcher are aware of the distortion because they have traveled in time. To Blackwood’s befuddlement, the Doctor quickly agrees to investigate Toynbee further. To his horror, Toynbee has solved one of the key equations necessary to manipulate time. Because Toynbee did not perceive the time distortion himself, he does not believe the Doctor’s warnings about the dangers of his work. Agent Hatcher is convinced by the Doctor’s concerns, but UNIT has no authority to intervene. On her own initiative, Lizzie sneaks back into Toynbee’s lab and sees him meeting with Malcolm. She is captured, but escapes thanks to another time distortion. Back at UNIT, the Doctor appeals to Blackwood, who is more interested in the continuing high-tech thefts. When the Doctor hears that the thefts have included a large number of beryllium clocks and ultra-high-precision mirrors, he deduces that the thieves are doing time manipulation experiments, which is enough to convince Agent Blackwood that the Morthrai are involved in Toynbee’s work. This is confirmed by Lizzie when she makes it back to UNIT. Agent Blackwood authorizes a team to secure Toynbee and his work. They fight their way to the laboratory to find Toynbee has completed his time machine under duress, having realized the Mothrai deception when Lizzie seemed to vanish earlier. Agent Hatcher is killed, but the Doctor uses the Toynbee Engine to create another distortion to undo her death, but Toynbee reveals that he rigged the engine to explode. But this turns out to be exactly what the Morthrai planned: they mean to send the engine back one hundred years, where the explosion will decimate the west coast, slowing human technological progress. The Doctor tries to deactivate the engine, causing more distortions, which leaves everyone but the Doctor, Lizzie, and Agent Hatcher frozen in time. The Doctor can prevent the explosion by redirecting the energy, but resolving the time distortions will restore time to the point where Hatcher died. She starts the redirection herself, sacrificing her life. The engine sends out a wave of time energy, and when it fades, the Doctor and Lizzie find themselves in the wilderness. The Doctor explains to a horrified Lizzie that redirecting the overload has sent them back in time two thousand years.