In 2005, the relaunch of Doctor Who was a huge success, and soon, a spinoff was commissioned, airing after David Tennant’s first season (and the new show’s second). The show-intended for older viewers than Doctor Who’s family audience-\would deal with a team of alien hunters, a reformed version of the Torchwood institute that appeared in the season finale of Tennant’s first season….and it would also feature, as it’s lead, Captain Jack Harkness, the Doctor’s companion from the latter half of the first season. In addition, Eve Myles-who had appeared in Doctor Who’s The Unquiet Dead as Gwyneth- would appear as Gwen, a police officer, and Naoko Mori would reprise her role as Doctor Toshiko from Doctor Who’s Slitheen two-parter. Joining them were Ianto Jones (Gareth David Lloyd) and Owen(Burn Gorman) Their base would be located near the time rift in Cardiff, also seen in Unquiet Dead.
The show would also have them face off against recurring savage aliens known as the Weevils, and the mysterious Billis Manger, as well as other threats and paradoxes spawned by the rift. They also dealt with a Cyberwoman, who was a partially converted girlfriend of Ianto.
In addition, something was revealed about Captain Jack as well. After his resurrection by Rose, he is unable to die, healing almost instantly from any injury (although still able to feel pain) and not being able to age as well. Plus, he possessed the Doctor’s severed hand, hoping that one day he’d come back to “fix” him.
The Doctor does actually show up at the end of the season, leading to the events of Doctor Who season 3’s master trilogy. ( Detailed Here: https://chrism227.wordpress.com/2016/09/18/doctor-who-history-donna-martha-mr-saxon-and-the-master/
Season two would introduce a new antagonist, Captain Hart, and also made Owen briefly immortal as well.
Also, Martha Jones, the Doctor’s season 3 companion, would join her friend Jack for part of the second season as well.
Unfortunately, the season ends with the death of Tosh and Owen, as Owen is killed by radiation and Tosh is shot by Jack’s long-lost brother, Gray. Although Gwen does marry her longtime boyfriend Rhys (Although she has feelings for Jack).
Torchwood next shops up in the Doctor Who story”Stolen Earth”/Journey’s End, helping the Doctor fight against Davros and the Daleks.
Things don’t get much better, however. All the kids on Earth start spouting cryptic phrases, and it’s discovered they’re being used by a three-headed alien creature-one that uses children as drugs, and captured twelve in the 40’s to cure Indonesian flu (an operation Jack was involved in, and not proud of). Torchwood’s base is targeted and destroyed due to Jack’s knowledge of the event, Ianto, Gwen and Rhys go on the run and Jack is captured.
The Aliens now demand 10% of all the Children of Earth or else they’ll destroy the planet. The guy used to handle this: John Frobisher-yes, played by Peter Capaldi, the actor who would eventually play the Doctor. Here he’s sort of a sympathetic villain.
When finally confronting the creatures, the aliens-the “456”-Ianto Jones is killed by their poison, devastating Jack.
Eventually, Jack figures out a way to defeat the 456 by reversing their signal. Unfortunately, he has to sacrifice his Grandson (Jack, as it turns out, had a daughter with a Torchwood member decades back). This is not a victory for Jack; although the 456 is defeated, he’s lost his Grandson, Ianto, Torchwood’s hub is destroyed and his Daughter hates him. He leaves Earth, and drowns his sorrows in a space bar, although the Doctor stops by to salute him and get him a date before he regenerates.
Meanwhile, back on Earth, things get weird again. Suddenly, nobody can die, even with massive injuries. As things go on, the Earth’s population starts to grow as well because of it. It seems everybody has Jack’s immortality (although without the healing unfortunately)-except Jack, who is now immortal. This turns out to be the result of Jack’s blood being used with a giant rock formation known as “The blessing”-creating a field around Earth.
Jack assembles a new Torchwood team with Gwen, Rhys, and CIA agents Rex Matheson (Mekhi Pfeiffer) and Esther Drummond (Alana Havins) to solve the Miracle and also evade those who want them silenced-and Jack dead (as he’s the only guy who can die).
The Miracle also causes chaos from not only the population not declining, but also it’s exploited by some Nasty humans for various means. Exploiting this miracle however are murderer Oswald Danes (Who couldn’t die at his execution) and his PR Lady, Jill Kitzinger, as well as Rex’s superior Fredkin (Wayne Knight), and CEO of a pharmaceutical corp, Stuart Owens (Ernie Hudson).
That’s right, Newman and Winston were in a Doctor Who spin-off.
Eventually, the “Blessing” is found and defeated by the Torchwood teams-ending the “Miracle” and returning everything to normal, and the whole thing was orchestrated by a mysterious group called the Family. They do this by ‘bloodletting’ Jack’s blood into the Blessing-which however has a side effect once things are over-making Rex immortal as he used a blood transfusion from Jack, to the surprise of Jack and Gwen.
…and apart from spin-off novels, comics, and Audios, that’s pretty much the end for Torchwood, although Jack is name-checked in a few later Doctor Who episodes.