Still smothering the umbrella stand, Marvar’s overcoat hung in the passage, its hem brushing the floor. Dyer stuffed it into Leandro’s games bag. He was halfway down the stairs when he stopped.

It was here, on the grey anonymous staircase, that Dyer had the idea. He reached out to the wrought-iron handrail, turned, and began to retrace his steps. Gripping the bag, he pushed open the door at the top of the stairs and walked, heart tripping, across the soft coral carpet. Suddenly, he saw a way to throw his enemies off the track.

The walls of the big domed reading room were covered in books. Seven had been reserved by Dyer. These volumes were stored with many reserved by other members in a free-standing open case in the centre.

Dyer stooped to a pile on the second shelf. He ran the back of his index finger down the spines, until it brushed against the wine-red copy of Uma Nova Luz Num Litoral Antigo, by Sergio Madrugada (University of Coimbra Press, 2017). He tugged the book out and took it into the French and German reading room next door. As he’d anticipated, this was empty, the regular tiny band of Modern Languages undergraduates no doubt attending a lecture downstairs.

He sat at the end of a long table by the window and undid the blue canvas games bag, delving under Marvar’s coat and pulling out Basil Bunting’s Collected Poems. He opened this to a poem on page 72, and, drawing on knowledge acquired in this very room nearly three decades before, he started to create a code in his notebook, from time to time referring to the poem’s last six lines, and altering certain letters into numbers.

His code established, Dyer dug out Marvar’s folder and withdrew the yellow post-it note. He tore off one of the two blank post-it notes on the back and, using his calculations and comparing these with Marvar’s – shielded in his left palm – he wrote out an altogether different algorithm on it, first one side, then the other, and finishing with the same words: ‘contrary to God’s will’?

He checked it over one last time, this false formula with his Bunting code copied out in what he hoped resembled Marvar’s handwriting. Then he tucked it back inside the green folder. As an afterthought, he slipped the third and last, blank, post-it note into his wallet.

Forty minutes had passed when Dyer folded Marvar’s original yellow piece of paper into the penultimate chapter of Professor Madrugada’s book, and returned to the stacks. He looked about. Three young women on the central round table, making notes. A chubby bald man in glasses, smiling to himself as he wrote a postcard. Reassured that no one was watching and there were no CCTV cameras to record his actions, Dyer reinserted Uma Nova Luz Num Litoral Antigo into the pile, and picked up his bag and left.