Hi scamp, I never watched the first series but my bloke made me sit through the latest series that was shown (I will never get back those hours that I lost)
It turns out that these island people (the others) live on a neighbouring island where there are proper houses and things. The leader guy is dying of some kind of spinal thing (I think) and that is one of the reasons why they want the dark haired fit guy called Jack (the doc). They are trying to play with the minds of the survivors and they know all sorts of random things about them, suggesting they have access to the outside world.
The woman called Juliet (the others) who looks like Jack's wife realises the leader is manipulative and tries to get Jack help in killing him. The last episode I saw ends up with him having control of the others.