Plot hole: Those people created for medical experiments cannot run. In fact they can barely walk, so how come they can climb nearly as fast as Rose? What's more, when you see them climbing, they seem to have little ability to coordinate hand over hand. Even with the delay brought on by the cat-woman-thing, they should not have been able to keep up with her.
Plot hole: Near the end of the episode, the part-human Doctor is said to have all of the memories of the original Doctor. If this is true, then the part-human Doctor should remember the time the original Doctor spent with Rose, so shouldn't commit genocide or need Rose to help him to not be a man of killing.
Plot hole: In "Aliens of London", it is established on a 'missing person' poster that Rose Tyler is approximately 19 years of age in March 2005 (The poster says 'missing since 6 March 2005'). This means that she must have been born prior to March 1986. However, in "Father's Day", which is dated 7 November 1987, Rose is still a baby in her mother's arms, when she should be a toddler aged approx two.
Plot hole: Davros said that the reality bomb would destroy all parallel universes. He fails in the Doctor's universe, but the Doctor said in an earlier episode that every decision creates a new parallel universe, like if Donna had walked out of the TARDIS with Jack, Rose, and the Doctor. She wouldn't have imbued herself with Time Lordness, so Davros would have succeeded. This means that all the universes, including the Doctor's one, should have been destroyed, because if the Reality bomb only succeeds in one universe, it would destroy all the others as well.
Plot hole: In this episode, the Doctor is said to have died during the events of "The Runaway Bride." As a result, he was not able to prevent the spaceship Titanic from crashing in London. It is later shown that southeast England was obliterated by the explosion. This falls far short of what the Doctor mentioned in "Voyage of the Damned", wherein he frantically repeated that if the Titanic crashed, the drive's explosion would wipe out all 6 billion people on the Earth (that's the entire human race at the time of the show's airing).
Plot hole: Martha tells the kidnapping couple to switch off all their engines so the Macra don't notice them. Yet during this scene, the car remains hovering above ground, meaning the engines must be engaged in some way, and the Macra should still hear them. And these things don't hover when deactivated - the car was shown to be parked on the ground at the start of the episode.
Plot hole: The Doctor leaves Martha a recording with instructions for her for when he's human. However, the flashbacks to the incident that led to him using the Chameleon Arch don't leave enough - or any - time for him to have made the recording, presenting his decision to use the device as a spur-of-the-moment one that he immediately acts upon.
Plot hole: When the Doctor and Missy, the latest incarnation of the Master, meet for the first time, she passes herself off as an android. Only later in the episode, after seeing the Gallifreyan hard drive that she has been uploading human minds to, does the Doctor realise that she is a Time Lady, and he doesn't realise that she's the Master until she tells him in the episode's cliffhanger ending. The problem here is that over the show's long history, Time Lords have been shown to have the ability to recognize each other instantly, an ability that makes perfect sense given their powers of regeneration. Previously in the new series, it was even stated that Time Lords can psychically sense each other, an ability demonstrated on-screen in "The End of Time." In "Dark Water", this does not happen, at all. Now, the Master has a history of using technology to block his/her psychic signal before - the Archangel satellite network from Series 3. However, at no point in this episode or the next one, "Death in Heaven", does either the Doctor or the Master even mention such technology as being used, leaving the mystery of how the Doctor didn't recognize Missy as a Time Lady at the very least a rather glaring hole.
Plot hole: The guy working for the Daleks offers the homeless men in Hooverville a dollar a day to go into the sewer because the Daleks need more people. Most of the people refused and one called it slave wages. If they were not getting paid until they came back, and since the Daleks were planning on experimenting on them, the people weren't going to come back; why not offer them a large amount of money big enough to entice them but small enough not to be suspicious?
Plot hole: When the Doctor realises that something is coming up from below ground, he tells Nasreen and Tony that at the speed the three transports are coming, the underground arrivals will reach the surface in 12 minutes. The rushed preparations that ensue, including hurrying from the drill hall to the old church and setting up a surveillance network outside, couldn't have taken less than 12 minutes to set up, especially given that they also had to: inform the others trapped inside the shield (Rory, Ambrose and Elliot), inform Rory and Ambrose that their significant others (Amy and Mo) were missing, run between the old church and the block of houses and gather supplies. And, lest we forget, there's also Rory and the Doctor arguing about what happened to Amy and Ambrose's initial skepticism as to what is occurring.
Plot hole: At the beginning, when the Doctor, Clara, Angie and Artie get off the TARDIS, the two kids are absolutely convinced that they're on the Moon, despite the Doctor explaining that they're actually at the Spacey Zoomer ride on Hedgewick's World, the greatest amusement park in the universe. The kids only realise they really aren't on the Moon when Webley emerges from inside of a fake rock formation, followed by the soldiers. The part of the room that the soldiers come from, which should have been fully visible to the time travellers from the beginning - in fact, they should have been looking directly at it when they leaned out of the TARDIS in the very first shot - looks nothing like the Moon and contains a sign for the Spacey Zoomer ride and a large map of the amusement park. (00:00:01 - 00:00:45)
Plot hole: After getting out of the Pyrovile escape pod, the Doctor and Donna start running back to Pompeii. In the process, they are somehow able to outrun what appears to be a pyroclastic flow. Pyroclastic flows can reach speeds of up to 700 kph, and should be impossible for them to outrun. (00:38:15)