Only self contained?

Well, we don't know if that was the finale markbc-2!

But yes, agreed. There were a few story lines for the main characters which were threaded through out the series (mainly Douglas' deceased wife and child, Justine's abilities and her son, Craig maturing as a character) but mostly, each episode was a self contained plot which would be solved in the end, or, sometimes, that would happen over two episodes. So yes, they did have back stories. I just wish the show had gone deeper into them!

Series 1: Douglas had personal plot about his past. Megan and Andrew were pretty much left as supporting characters without much need for a backstory.

Series 2: Megan and Andrew have gone, and are never heard of again! Justine and Craig arrive as Douglas' new colleagues. We learn Justine has psychic abilities and this is developed a little through the episodes, as is her family life with her son. Douglas' past is dipped into again, a little.

Series 3: Justine's abilities are developed more, and we discover her son shares them (though this plotline was never visited again). Craig grows up as a person. Douglas' attempts to move on from his past, and I think even tries a date in 'Sleeper'.

Series 4: Justine and Craig have vanished without a trace nor mention. Douglas as a character is developed more.

Quick summary :)