This was the first episode to introduce the series' finalised cast: Lenora Crichlow, Russell Tovey and Aidan Turner with Jason Watkins and Annabel Scholey in the main supporting roles.
Unable to either communicate or even effectively make herself known to the succession of tenants who rent it, she is close to succumbing to "the worst thing about being a ghost...
Mitchell, a former young soldier, is now a vampire for whom "death isn't the end, but the beginning" and who harbours terrible guilt over his victims.
Annie must deal with her past: most specifically, the fact that her former fiancé Owen (also the owner of the house where she, Mitchell and George live) is now engaged to her former rival Janie Harris.
With Mitchell's help, he tries to use the woods but finds them full of people: the only safe place to transform is at home, although he smashes the furniture and upsets his housemates.
[1] Russell Tovey (George) and Dylan Brown (Seth) were the only cast members from the pilot episode to renew their roles for Series 1.
Annie (now played by Lenora Crichlow) was an ostensibly sunnier and more scatterbrained character than had been suggested by the more awkward, dour characterisation from Andrea Riseborough in the pilot; while Aidan Turner's take on Mitchell was more relaxed and smooth in presentation.
Most notably, the recast Herrick (originally played by Adrian Lester) was altered in multiple respects including speech style, race and general demeanour.
Series creator Toby Whithouse has stated that he considers the story and events in The Monsters Within to be canonical, even though the production style and casting were noticeably different.
The events of The Monsters Within precede those of Flotsam and Jetsam by an unspecified period, but probably no more than days or weeks as Mitchell's killing of Lauren and its immediate aftermath is still relatively recent.
The cold open of Flotsam and Jetsam restated, in a highly compressed form, several events and plot elements either shown or referred to The Monsters Within.
It also introduced elements not covered in The Monsters Within, including Mitchell's own recruitment into the vampire world by Herrick and greater illustration (via montage) of Annie's experiences of loneliness, resentment and disaffection following her own death.
Notably, there was no attempt to restage the initial meeting of Mitchell, George and Annie (the main episode began with all three relatively comfortably established as housemates), George and Mitchell's original application for jobs at the Bristol hospital, or Herrick's sumptuously staged address to the vampires in the Bristol basement.
Some of the content of the latter (which was now too grandiose for the new conception of the character) was reworked into dialogue within "walk-and-talk" scenes between Herrick and Mitchell in and around the hospital grounds.
The abandonment of this subplot also meant the loss of a significant scene in which George confronted Julie's abusive new boyfriend Peter and succeeded in intimidating him while also holding off his own werewolf urge to kill and eat.