In this BBC press release, Being Human creator Toby Whithouse introduces Series 5:

Whenever we sit down to storyline a new season of Being Human, we try to find a single headline – unofficial and usually never stated – that encapsulates the series arc. It’s more of an ‘aide memoire’ for us, something that articulates our ambition and intention.

Series One told the story of Mitchell, George and Annie settling into their new home and the beginning of their (ultimately futile) attempt the ape humanity and live a normal mundane life. In my mind it was titled ‘There Goes The Neighbourhood’.

In Series Two, our heroes were being hunted and manipulated by a shadowy group of religious zealots who had perverted the word of God to suit their own agendas, believing the eradication of supernatural creatures was a divine mission. I called it ‘God Loves, Man Kills.’

Series Three dealt with the aftermath of the massacre Mitchell committed in Box Tunnel the previous year and his ultimate destruction at the hands of ‘The Wolf-shaped Bullet’.

And Series Four detailed the vampire myth of ‘The War Child’ – George and Nina’s orphaned baby – and her part in destroying the vampire aristocracy.

When we started work on Series Five we gave it the title ‘The Greater Good’.

Every year we try and up the ante. Blowing Mark Gatiss and a baby up at the end of Series Four was good, but we could do better. We wanted to tell a story that was even greater, even more labyrinthine and epic than anything we’ve done before. Slowly a story about sacrifice and misplaced courage started to take shape. Our heroes would be driven to compromise their own fragile humanity to safeguard the rest of the world; and less scrupulous characters would endanger the lives of others in pursuit of their own agendas.

Then, as other elements started to develop, we toyed with ‘He Will Rise’ as our headline title. The merits of our main cast(s) have been well documented, but we have also been lucky enough to have some of the finest actors the industry has to offer playing our Big Bads – Jason Watkins, Lyndsey Marshal, Donald Sumpter, Andrew Gower, Mark Gatiss; and this year we’ve been blessed to have Phil Davis join us, as the repulsive and cruel Captain Hatch, arguably our biggest villain ever. It’s a performance of such delicious evil, you’ll be left with your jaw on your chest and your breakfast on your lap. He’s joined by Steven Robertson as the mysterious Mr Rook, the sinister Man in Grey we met at the end of Series Four, and Colin Hoult as the deluded and volatile Crumb. A newly recruited vampire, he describes himself as ‘the world’s worst nightmare: the victim that suddenly gets super powers’.

But in the end we settled on ‘The Trinity’, because this was the first entire series with our new cast. Thanks to the brilliance, enthusiasm and sheer elemental talent of Damien Molony, Kate Bracken and Michael Socha; it was their skill and passion that would stop me rocking and dribbling and draw me out from under my desk to actually write the scripts.

And so this series title belongs to them. The new heroes of Being Human. The new trinity.