A temporally active race, The Doctor’s encounter with the Squall was interesting as he and his companions actually caused the crisis while trying to investigate it.
A race of pan-dimensional parasites, the Squall normally exist in other planes of reality, similar to the more powerful Chronovores, but they can only access this universe when a temporal rift is created, allowing them the chance to enter the real universe, where they can ‘feed’ on the psychic energy of others to gain greater power and produce more of themselves. A hive mind, the Squall start off as simple beasts but become more intelligent as more of them are unleashed into this universe, their minds gaining power as they come together until they can even ‘hack’ the TARDIS’s telepathic circuits, allowing them to communicate with The Doctor and his friends inside the ship.
Although the Squall attacked Earth in 1910, The Doctor was alerted to their presence when the Eleventh Doctor, Amy and Rory were drawn to London in June 2789 by a distress signal. Tracking the signal to its source, the three discovered a centuries-old android in the Thames that had just been salvaged by an archaeology team, the android attempting to pass on a message to The Doctor about the time experiments of Professor Gradius and the presence of the Squall before it apparently ran out of power. Having determined the date that the android would sink, The Doctor departed to investigate the Squall in the past, leaving Amy and Rory to find Professor Gradius in the present.
Visiting Professor Gradius’s laboratory, Amy and Rory discovered that she was dead, but quickly found another ally in the form of her robotic assistant RVN-73, Amy nicknaming him ‘Arven’ for convenience’s sake. Although Arven was able to reveal that Gradius had been killed by the Squall, they were forced to subsequently retreat to the time machine that Gradius had been working on when the Squall resumed their attack on the lab, travelling back to 1910 to meet up with The Doctor. Ironically, when Amy, Rory and Arven used Gradius’s time machine to travel back to 1910 to escape the Squall, they actually caused the rift that would draw the Squall to London in the first place, landing in London on 13 October 1910 and remaining underground by hiding in the sewers for three days until The Doctor arrived in that time period (Rory was briefly concerned that they’d made a bad situation worse by causing a situation that they’d already learned about, but The Doctor assured him that such paradoxes were really nothing serious given the complex nature of time).
Meanwhile, The Doctor had discovered a new ally in 1910 in the form of Professor Angelchrist, a scientist who had spent his life working to track down alien technology and defeat alien attempts to conquer Earth. With Angelchrist’s research helping The Doctor identify the Squall’s feeding grounds – they generated a low-level telepathic field that had prevented anyone else realising that they were present, but Angelchrist had been immune as he had experience with other-worldly matters, The Doctor was able to track down the time-ship in time to rescue Amy, Rory, and Arven, using the sonic screwdriver to disorientate the Squall long enough to drive them away.
Retreating to Angelchrist’s house to use some of the alien technology that he had assembled over the years, The Doctor was able to turn a top hat into a psychic amplification beacon that would enhance the signal given off by his mind, allowing him to lure the Squall back to the original rift, although Arven was forced to sacrifice himself to end up in the Thames as he had originally so that the humans could escape. Luring the Squall back to the time ship, The Doctor was then able to set the ship to overload as the Squall tried to attack him, destroying the rift while he was rescued by the TARDIS, which he had programmed to home in on his mind at the moment the implosedition occurred (Although he had claimed that he couldn’t use it earlier to trick the Squall into thinking that he was more vulnerable than he was). With the rift closed and the Squall destroyed, The Doctor took Angelchrist on a brief trip to the future so that they could recover Arven, The Doctor transferring him into a new body and then leaving him with Angelchrist so that Arven could make a life for himself without worrying about the legal issues he might face as an independent A.I. in his time, as well as giving Angelchrist a friend in his old age.