The Tenth Doctor (wonderfully played by David Tennant) was probably one of the most popular incarnations of the Doctor of the new series (and possibly even overall). He was charismatic, charming and funny but he also had an edge when it came to confronting villains which made for an extremely interesting portrayal.
The Tenth Doctor also had the good fortune of having some brilliant storylines during his tenure. As well as the season-long story arcs, his episodes were often of high quality. However, there were instances where some of his plot lines felt unresolved or abandoned and so here we've collated the top ten.
10 The Unexplored Journeys Of Martha Jones
Martha Jones was a great companion who had the unenviable task of following Rose Tyler, who both the audience and the Doctor had grown to love. Fortunately, though, Martha was more than capable of holding her own, frequently demonstrating her unlimited knowledge of medical skills and saving the Doctor and planet Earth on multiple occasions.
When she left the TARDIS to look after her traumatized family, she did return briefly in the next season. However, the way she left the show seemed to imply that she could come back at any time; Martha even left the Doctor her cell phone. She could have even played a Brigadier-esque role, popping up infrequently to support multiple Doctors.
9 "Blink"'s Unseen Adventures
The Doctor-lite episodes have an unusual habit of either being extremely good or terribly bad. In "Blink"'s case though, it was one of the best episodes of Season 3, a feat even more impressive considering the Doctor and Martha barely featured.
When they did appear though, they were always in the middle of some adventure. The first time they popped up, they were stranded in 1969 after watching the moon landing 3 times. The second time was even briefer and involved migration, a red hatching, four things, and a lizard. It definitely sounded like an episode worth watching.
8 The End Of "The Age Of Steel"
The Cybermen's first appearance in the modern series of Doctor Who was a bit of a mixed success. The Cybermen themselves were realized almost perfectly, a gruesome blend of flesh and machine. However, the fact that it all happened on a parallel world left viewers wondering what happened to the Cybermen in our reality.
Another unresolved issue was that at the end of the episode, the Doctor had defeated one cyber-conversion factory but there were still thousands active across the UK. While this was slightly addressed in the season 2 finale, it would have been much more exciting to see exactly how the parallel Earth fought back against the remaining Cybermen.
7 Elton Pope And Sally Sparrow
The Doctor-lite episodes often left multiple unresolved storylines as a result of their unique format. One such unresolved issue is that of the one-off companion. Doctor Who has demonstrated multiple times that even one encounter with the Doctor is enough to change your life forever, for example, Rose Tyler, Amy Pond, Donna Noble, etc.
Sally Sparrow and Elton Pope appeared to be the exceptions. There was never any mention of them either again after their sole appearances, which is odd considering they had quite a large role to play in the episodes themselves. Even if they returned for a brief cameo, it would be nice to see how their lives turned out after meeting the Doctor.
6 Lady Christina de Souza
Lady Christina is very similar to Elton and Sally but she gets a separate entry to herself because of the way things were left between her and the Doctor. Unlike Elton and Sally, Christina actually met the Doctor for an extended period of time and so was even more of a likely companion.
She was smart and quick-witted and more than a match for the Doctor. She was also a criminal, which would have been extremely interesting to see play out over a season or two. Even her ending was ambiguous as the Doctor last saw her fly away on a double-decker bus over London. Christina would have been great companion material.
5 Queen Victoria Is A Werewolf?
In only the Tenth Doctor's third onscreen adventure, he and Rose arrived in 19th century Scotland and encountered evil monks, an alien werewolf and of course, Queen Victoria herself. The monks' plan was to infect the Queen with the werewolf gene so that the Monarchy of the Wolf could reign.
The Doctor defeated the werewolf just in time but after the wolf's last attack, Queen Victoria was found to have been scratched. She claimed it was a splinter from the door but refused the Doctor's help. The Doctor then suggested the gene may be lying dormant until the early 21st century... This seemed like too good an opportunity to miss but it was never mentioned again.
4 The Midnight Creature
"Midnight" was one of the best episodes of Season 4. The Doctor had gone on a special planetary sightseeing trip across a diamond planet called Midnight and almost the entire episode happened onboard a futuristic bus.
Since it's Doctor Who, a mysterious creature began knocking on the walls and then entered the vehicle. The creepy part was no one ever saw what the creature looked like. It possessed people's speech and took them over but even after the creature was defeated, no one, not even the Doctor, knew what it was or how it survived in the planet's lethal sunlight.
3 The Lazarus Technology
Season 3 introduced an interesting concept: if you change human DNA into something almost unrecognizable, is it still human at its core? Professor Richard Lazarus was the unwitting guinea pig in this experiment as his de-aging machine altered his DNA and turned him into a scorpion monster.
Lazarus's technology popped up again in the season finale when the Master used it to age the Doctor 900+ years. However, for such an interesting plot device, it vanished after those couple of episodes. In the wrong hands, it could have been a very powerful weapon and so it seemed odd that it was never brought back.
2 The Fate Of The Toclafane
When the Doctor, Martha and Captain Jack Harkness visited the year 100 trillion, they encountered the last survivors of the human race. Desperate to survive, the humans had built a rocket to take them to a mysterious object they christened 'Utopia'.
Unfortunately, 'Utopia' didn't exist and so they cannibalized themselves in order to survive. When the Master found them, he built a paradox machine to enable the mutilated humans to go back in time under the guise of 'the Toclafane' and slaughter their ancestors. When the paradox machine was destroyed, the Toclafane were left alive at the end of the universe but were never heard of again.
1 The Doctor's Daughter
This is probably the biggest unresolved storyline ever in Doctor Who's history, let alone the Tenth Doctor's. On the planet Messaline, the Doctor's genetic imprint was taken and used to create a new being based on his DNA. The result was Jenny, a young woman biologically related to the Doctor.
The Doctor took a while to warm up to her as Jenny was initially born to be a soldier. However, Jenny soon followed in her dad's footsteps and the two began to bond. Unfortunately, during the episode's climax, Jenny was shot protecting her father and died in the Doctor's arms. After the Doctor left, Jenny was revived but viewers never got to see any of her adventures, losing one of the series's finest characters.