Peter Lovesey - The Last Detective

If proof of Mat's commitment were required, it came when he put down the cake half-eaten and suggested they started. Diamond told him there was plenty of time to clear his plate.

'I can't. I'm too excited,' Matthew admitted.

Diamond's self-control wavered. 'Pass it across, then.'

At 4.20 pm, they left the Colonnades, crossed Stall Street and entered the Baths. To reach the ticket office, it was necessary to pass through the Pump Room, the meeting-place of Georgian society that now serves as a restaurant. The tea-time ritual was fully in session, every chair occupied, the waitresses in their black waistcoats, white blouses and aprons trying zealously to keep up, and the trio at the near end lustily performing the Toreador music from Carmen. It was a relief to penetrate to the more serene atmosphere beyond.

Not many visitors were entering the Baths at this stage of the day. The woman in the ticket office warned them that the exhibition closed to the public at 5.00. Attendants would ask everyone to leave. Diamond gave a nod of understanding. As soon as they were out of earshot, Matthew, the veteran interloper, confided to Diamond that he knew hundreds of places to hide.

Diamond didn't care to admit that he'd never previously made the official tour of the Baths. Two terms of Latin in his youth had killed any interest in the Romans. Once he had attended a civic dinner in the Pump Room, preceded by cocktails beside the Great Bath; looking up to admire the lighting supplied by flaming torches attached to the columns, he had tripped on the uneven paving and spilt most of his drink down the dinner jacket he'd hired for the evening.

They came first to the remains of the temple of Sulis Minerva, picked out by discreetly sited lighting, so that the weathered limestone effigies of the gods glowed red-gold on the altar. The tourists down there were lingering to gaze, if not to read the guide-notes, but Matthew, striding through as if it were his home, said, 'You don't want to waste time here. Andy covered this bit a month ago. He's doing the Great Bath this week.'

They moved along a walkway and down several flights of stairs, taking a series of turns that confused Diamond's sense of direction until they passed a window that looked down on to an open-air bath. The surface of the water was bubbling. 'That's only the sacred spring,' Matthew mentioned dismissively, seeing Diamond hesitate. At a still lower level, they heard a steady rush of water and saw the arch where the overflow from the spring tipped out as a miniature waterfall.

Ahead was daylight and the Great Bath, its blue-green rectangle overhung with steam. After the spotlights in the tunnelled approaches, the sense of space and light could not fail to impress. The Bath itself was some seventy feet by thirty, with steps down to the water. Rows of columns on stone piers surrounded it, supporting a canopy for the flagstoned aisles where Romans once promenaded, watching the bathers. The stretch of water was open to the sky. Visitors stood in ones and twos along the aisles, staring up at the columns and the sculptured figures mounted above them. 'Most of it's Victorian,' Matthew informed Diamond. 'The Roman stuff barely comes up to your knees.' His education had profited from his trespassing in the Baths.

Diamond wasn't there for the architecture. A group of young people had gathered at the far end. Their style of dress and their absorption in conversation, rather than the surroundings, confirmed them as students. The lecturer had not appeared yet.

For the moment, Diamond had no need to get close to the students. Around the sides of the Bath, under the canopy, were a series of recesses where miscellaneous bits of masonry were displayed on stone plinths. Most were too low or too narrow to be useful to someone of Diamond's size, but at the centre of the south side was a larger bay that housed an assortment of broken pilasters and columns. It looked possible to get behind it without attracting attention.

He and Matthew strolled casually around the pool until they were level with the bay. After glancing around, he touched Matthew's arm and steered him behind the plinth. They didn't even need to crouch.

Visitors continued to drift by for the next ten minutes, and then two of the security staff came through, evidently to warn any lingerers that the exhibition was about to close. Mercifully, although they passed quite close to the plinth, they didn't look behind it.

By degrees the surrounds of the Bath emptied except for the history class and its hidden observers. The daylight was starting to fade. High above the Great Bath, the figures of the Roman emperors appeared more dramatic against the sky.

'You okay, son?' Diamond enquired.

Matthew nodded.

A moment later, footsteps clattered on the flagstones quite close to them, steps too brisk for a sightseer, even a belated one trying to get round. And it wasn't one of the attendants.

'It's him,' Matthew whispered. 'Definitely.'

Andy Coventry passed within a few feet of them on his way around the perimeter to his students – his head and torso visible from their vantage-point, the shoulders so broad and well-muscled that the black teeshirt he was wearing seemed like a second skin. The striking feature was the bleached mass of hair swept back from the forehead over the skull in the style of some sports idol of the 1950s.

Diamond said, when it was safe to speak, 'Let's watch for a bit.'

There was some lively barracking from the students when Coventry approached them. He was probably ten minutes late. He opened a sports-bag and took out what presently proved to be a number of steel measuring-rules and handed them round. His voice was audible only in snatches across the water, but it was clear that he was issuing instructions, setting the class some kind of project. He knelt beside one of the original Roman piers supporting a column and measured its length and height. There was some discussion about the additonal masonry used to reinforce the structure that had once supported a timber roof. The students had produced clipboards and were recording the information. Coventry started assigning them in pairs to the six main piers along the north side of the bath.

In a few minutes, all of the students were busy, measuring and taking notes. Satisfied, apparently, that they were usefully occupied, Coventry picked up his bag and strolled away from the class towards one of the exits at the west end.

Diamond put a restraining hand on Matthew's shoulder. This was going to require the stealth of a professional. He left the boy, stepped back into the shadows and crept off in the direction Andy had taken. Conscious of his size, he moved with a lightness of step more appropriate to a much slimmer man.

A suspicion had dawned in Diamond's brain even before Andy had appeared with the sports-bag. The next few minutes, he sensed, would be crucial to the investigation he had started all those weeks ago and was pursuing to its climax.

The need to remain unnoticed was essential, and so was the need to see what Andy Coventry was up to. It meant venturing into a complex of warm and cold baths at the west end of the Great Bath – with a high risk of discovery now that no visitors were left. He passed through the open door. Making use of every feature of the building that offered the possibility of cover, he approached the circular cold plunge bath known as the frigidarium and stared around its perimeter for a sighting of his man. The subdued lighting was a mixed blessing.

He seemed to have lost the trail already. The walkway system lined with plexiglass sides began again in this section. All he could see as he peered over the handrail opposite was the site of another bath, practically empty of water. Obliged to move on into a section still more in shadow, he found himself looking down on a sunken area where columns of copper-coloured bricks stood in ranks like the Terracotta Army discovered in China. He knew what it was from postcards he had seen: an early form of central heating. The columns had once supported a floor, enabling hot air from a charcoal-burning flue to circulate in the cavity. Above, in their Turkish bath, Romans had once sat and sweated and been oiled, scraped and massaged. The hypocaust, as it was labelled, was one of the most notable features of the Baths, mainly because of its function, and also for the strange, unforgettable spectacle of more than a hundred of these knee-high columns, filling the floor space in symmetrical formation, no less impressive for being worn and damaged, A chromatic mix of copper and ochres that time had rendered into what could easily have passed for a masterpiece of modern art.