Need a quick recap?
Captain Jack Harkness- Same old Jack, only it's 5 years after COE:day 5 and he and Ianto have had their lifelines linked by the Doctor - see Eternity. Still together with Ianto, though sometimes joined by Loz and John.
Ianto Jones- After COE:day 4, he was saved by Jack and the Doctor, again see Eternity. The consequences of his salvation are seen in chapter 3. His sister Rhiannon is now fully aware of his 'extended lifeline' after chapter 3. He and Jack are still together, though sometime he allows John and Loz to share.
Gwen Cooper- Now in charge of the newly rebuilt Torchwood. She is still married to Rhys, and they have a 5 year old daughter named Isabella, introdced in chapter 1.
Captain John Hart- Came back to see Jack just after the old Hub was destroyed in COE. As Jack and Ianto were gone and Gwen needed help, she recruited him to work for Torchwood. Currently dating Loz (and occasionally Jack and Ianto following chapter 9)
Lizzie Parker- Tech/Computers expert who first appears in chapter 1. Her background is explored in chapter 8, explaining how she managed to get the attention of Torchwood and eventually be recruited. Currently dating Nicholas.
Dr. Adrian McAuley- Former emergency department doctor, recruited by Gwen and John as the new Torchwood medic after his assistance in stopping an alien causing chaos in the hospital he worked at. First appears in chapter 1. His backstory and recruitment is expained in chapter 2.
Loz- Former bounty hunter from the planet Liegen. Originally sent to arrest Adrian in chapter 2, he was targeted by his employers after refusing to bring the doctor in. Now working with Torchwood. More of his history in chapters 4 and 5. Currently dating John (and occasionally Jack and Ianto following chapter 9)
Nicholas Harrington- Accidentally brought through the rift from 1889 in chapter 6. He was cursed back in the his own time into spending his full moons as a werewolf. Not working for Torchwood, though he sometimes assists them. He and Lizzie are dating.