The massive flood triggered by the tsunami finale of the previous boxset of the God Among Us trilogy has left disaster in its wake as the third instalment opens. Cardiff Bay is in ruins, hundreds are dead, others are missing, and the shell-shocked survivors are hunkered down in inland refugee camps. But when it comes to the expected emergency response, the authorities’ efforts are feeble – so volunteers do their best to fill the gap and deliver whatever help they can muster. The government is putting more effort into an official enquiry into the cause of the calamity, but their efforts are frustrated, as important documents are redacted and key witnesses report they are suffering from amnesia.

This makes for a terrific dramatic setting in its own right, but the context of dislocation and disorder provides an unusual backdrop against which the soon-to-be-answered question (“who will win the battle to decide the fate of planet Earth?”) can play out to its dramatic conclusion. A common experience for most of the key characters here is being pushed far outside their comfort zone, as they are forced to deal with the chaos left behind by the receding flood waters. The most obvious candidate is Sergeant Andy Davidson (Tom Price) promoted to the thankless position of head of the Disaster Recovery Commission and immediately struggling to marshal the inadequate resources at his disposal and meet the demands of the job.

Opener A Mother’s Son by Alexandria Riley explores the poignant story of flood survivor Bethan’s determination to discover the fate of her missing offspring (despite the seeming indifference of the authorities) and Orr’s (Samantha Béart) misconceived efforts to bring comfort to the grieving. The political fallout from the disaster reverberates throughout the episode, as Bethan (Mina Anwar) clashes with the Commission and Yvonne Hartman (Tracy-Ann Oberman) makes a pitch to unseat Davidson and seize control of the recovery effort.

Anwar’s portrayal of the distraught Bethan is emotionally charged and affecting and, in a series which stresses the ensemble nature of the Torchwood cast, is one of several standout guest appearances. While all of the regulars are dependably strong, pride of place in the acting stakes must go to Jacqueline King. She’s provided with the strongest and best written dialogue that God has enjoyed in the series, and in response she delivers her most irresistible portrayal in the whole trilogy of the doubting deity. Tom Price also deserves a special mention. He’s clearly having huge fun portraying Andy as a copper completely out of his depth but trying to do what he thinks is the right thing regardless.

Fantasy thriller ScrapeJane by Robin Bell (who sadly passed away in May) steps away from the concerns of the wider story to deliver a more traditional standalone Torchwood tale, and a very effective one too. ScrapeJane is a fictional creation, invented by wily local historian Meredith to encourage tourists to visit Cardiff’s hidden dark corners. A spectral murderer, eager to target new victims, ScrapeJane has become the subject of a social media frenzy, her “story” weaved into a mesh of urban myths. As they are drawn into the mystery and forced to investigate without any of the usual Torchwood resources, Colchester (Paul Clayton) and Ng (Alexandria Riley) make a winning pairing. Bell’s script is full of chilling and frenzied encounters with otherworldly forces and, as it unfolds with a great sense of pace, provides an intriguing temporary change of direction.

There’s a grim plausibility to the events of Tim Foley’s Day Zero, which returns the focus to the worsening Cardiff crisis amid an acute shortage of fresh drinking water. With the taps running dry, events quickly spiral out of control as the city’s desperate and thirsty residents seek water from any source, whatever the risks. There appears to be a single drinkable supply left within the emergency zone, and everyone, including Price’s Committee and the remnants of Torchwood, want to take control of it. It’s a tense and fraught tale, in which human thoughtlessness is shown to have terrible consequences.

James Goss steps up to deliver the sign-off for eleven episodes of build-up – and does so very effectively in the finale Thoughts And Prayers (its title an echo of the empty aphorism frequently used by politicians in the US in response to gun outrages). The stories leading up to this point have shared the running themes of a loss of self-belief on the part of the God living “among us”; the growing ambitions and manipulative agenda of the secretive Committee; and the struggle to re-establish and reinvigorate Torchwood. All of these are addressed in a fast-moving tale, which includes a welcome return to the remnants of the Hub, and some moments of great tension as epic forces clash.

The scale and substance of the God Among Us storyline has merited its treatment as a trilogy, and with matters brought to a creditably strong conclusion here, there’s already an enticing premise for future adventures in which there will be no easy victories for a Torchwood team hampered and harried at every turn.