A parachutist falls to Earth. Toby Kramer, a wannabe video-artist, is visited by one Zenna Briggs in his basement flat. Zenna represents the James and Zenna Briggs Arts Foundation, and wishes to see Toby’s work in progress: a film about a vanished IT contractor named Simon Vines. It mixes short interviews with Simon’s ex-wife Ally, his landlady Mrs Wales, and friend Sadaqat who lives in a psychiatric ward and believes that a staff-member, Doctor Marinus, is an incorporeal being. Zenna is captivated by Toby’s ‘Portrait of a Missing Man’ and gives Toby a fat banker’s draft.

Three months later. Zenna visits Toby for an update. Toby confesses he hasn’t found Simon Vines; but has identified a girl, Amber Jacquemain, whom Simon Vines met while visiting Sadaqat. Unfortunately, Amber has also vanished into thin air. Zenna guesses Simon and Amber eloped, but then Toby shows her video clips from Amber’s iPhone: this hedonistic montage includes Amber describing a dream of a sunken garden, where she’s innocent of certain crimes. Zenna hands over more money and leaves.

March. Zenna now wants to see a return on the Foundation’s investment. Toby claims that Simon and Amber were abducted. Sceptically, Zenna asks for proof. Toby shows new footage of Sadaqat, who now asserts that the missing man and woman were the victims of a hunter who uses the dream of a peaceful garden to entrap the tormented. Zenna now tells Toby that the Foundation wants nothing more to do with these paranoid delusions.

His mind unspooling, Toby Kramer wanders the city’s edges until he comes upon a bright door in the pillar of a flyover. Toby goes through, and finds a sunken garden – and Simon Vines, or at least a frozen image of him which, when touched, bursts into brief, staticky, verbal life. The mysterious Marinus enters. Toby accuses her of somehow incarcerating Simon in this place. Marinus denies the charge. A living hologram of Amber appears and gives an equally cryptic account of herself before freezing. Toby asks what Marinus gains from this: Marinus demands that the garden’s maker step forward…

The garden, we learn, is an occult engine built by Zenna in the dusk between life and death. After half a year in world-time, nothing is left of the visitors but undying moths. Zenna reveals her back-story from an orphaned half-caste girlhood in the British Raj to an undying architect of the occult in the twenty-first century. Marinus threatens to detonate her own powers, thereby destroying the sunken garden and everyone in it, unless Zenna agrees to this deal: allow Toby free passage back to the world; award Simon and Amber a ‘retrial’; and allow Marinus to dismantle the garden. Zenna agrees to the deal.

Simon and Amber reveal their back-stories. Zenna tells Marinus that the deal is off, so Marinus breaches the sunken garden and collapses. Zenna makes a second announcement: she is here not in body but only in spirit. Her corporeal self is safe in Toby’s basement flat, through the vertical pond. She intends to build another sunken garden, rendering Marinus’ sacrifice futile. In the last possible moment, Toby exits the garden via the vertical pond, but there is one serious catch…

Some weeks later. Toby ruminates on his awkward fate as a man trapped inside Zenna’s now-mortal body. He replays a film, the last that he – or ‘she’ – will ever shoot: it shows Portia Jacquemain, Amber’s mother, describing how she learnt that Amber’s body was found; and recalls a day, long ago, when she and her daughter shared a moment of pure understanding. Next up is Simon, large as life, discussing his grief and self-blame over the cot-death of his daughter. He is dressed in parachuting gear, and Sadaqat and Mrs Wales wave him onto a light aircraft. Up it climbs. Out he jumps. Look at it, this… massive, unfair, beautiful, cruel, miraculous… World-Machine. Look at it. And you think, ‘I’m a part of this, too.’