Warning: spoilers ahead for Doctor Who season 14, episode 8.

Summary

• Doctor Who's bi-generation twist means David Tennant's Fourteenth Doctor is available to help, but he doesn't do so against Sutekh.
• David Tennant's Fourteenth Doctor is killed by Sutekh during the Death Wave.
• Future Doctor Who stories must still explain the Fourteenth Doctor's absence, posing a challenge for the series and its continuity.

David Tennant's Fourteenth Doctor has a very good excuse for not helping in the battle against Sutekh during Doctor Who's bi-generation twist in "The Giggle" changed that by allowing David Tennant's Fourteenth Doctor and Ncuti Gatwa's Fifteenth Doctor to coexist - one relaxing with the Nobles, the other exploring time and space.

Immediately, bi-generation risked a Doctor Who plot hole. Because the Fourteenth and Fifteenth Doctors occupy individual timelines, there is nothing to prevent them working together. Fourteen may be officially retired, but that's unlikely to stop him saving the world if a major threat emerges, and Sutekh is nothing if not a major threat. This poses the question of why Ncuti Gatwa's Fifteenth Doctor receives no help from his predecessor in Doctor Who season 14's ending.

The Fourteenth Doctor Is Killed By Sutekh's Wave Of Death In Doctor Who Season 14's Finale

The Fourteenth Doctor Is Turned To Dust

The Fourteenth Doctor certainly would have assisted in Sutekh's defeat, but Tennant's latter version of the Time Lord is killed during the God of Death's cosmic massacre. Sutekh revealed himself at the end of Doctor Who season 14's "The Legend of Ruby Sunday," and immediately begins wiping out life across the universe when "Empire of Death" begins. The Fifteenth Doctor is amazed that he and Ruby are left alive, and eventually figures out that Sutekh is so curious about the identity of Ruby's mother, he is refraining from dusting them until the mystery is solved.

Fifteen realizes, "No wonder he's keeping us alive - to figure out the answer: who is she?" By the time the final showdown begins, the possessed Mel confirms Fifteen and Ruby as "the last two creatures in existence." This proves David Tennant's Fourteenth Doctor is, at some point offscreen during "Empire of Death," killed by Sutekh along with everyone else. Fifteen is the only Doctor that Sutekh needs alive, meaning Fourteen - and all other incarnations of the Doctor - die.

Future Doctor Who Stories Must Still Explain The Fourteenth Doctor's Absence

Doctor Who Gets Away With Its Fourteenth Doctor Plot Hole... This Time

In this instance, David Tennant's absence from Doctor Who makes perfect sense, but the initial problem caused as a consequence of bi-generation remains, and will inevitably rear its head in future episodes. By the end of Doctor Who season 14, everyone killed by Sutekh is revived, meaning the Fourteenth Doctor is back in Donna's garden sipping Prosecco and boasting about the time he "snogged Madame de Pompadour" (probably).

Based on Doctor Who history, it will not be long before another devilish villain attempts to wipe out all life on Earth, and when that time comes, the "why isn't the Fourteenth Doctor helping?" question will arise again. Doctor Who's challenge in season 15 and beyond will be to continue ing for the Fourteenth Doctor's absence in these situations, and there are only so many excuses that can be made before the trope wears thin. Doctor Who gets away with it in "Empire of Death," but sooner or later, will need a more permanent solution to its Fourteenth Doctor problem.