'Most Reverend Doctor Mirabilis, it is good to meet you again.'

The fellow looked up, his eyes milky blue like those of a cat. He studied Cranston then stared past him at Athelstan.

'Do I know you?' he asked. 'Do you wish to buy my physic?'

'Samuel Parrot,' continued Cranston, 'I would not buy green grass from you in the spring.'

The fellow's eyes shifted to right and left.

'Who are you?' he whispered.

'Surely you have not forgotten me, Mirabilis?' Cranston murmured. 'A certain case before the Justices in the Guildhall about physic which was supposed to cure. Instead, it made men and women sick for weeks.'

The famous Doctor Mirabilis stepped closer.

'Of course!' His face broke into a gap-toothed smile. 'Sir John Cranston, coroner!' The smile was hideously false. 'Is there anything I can do for you?'

'Not here,' Cranston said. 'But Piper Alley, Nightshade House. You can lead us there?'

The physician nodded and, scooping up his philtres and potions into a leather sheet, led Cranston and Athelstan from Whitefriars down a maze of streets so narrow they continued to lead their horses.

'How does he do it?' Athelstan whispered.

'Do what?'

'The bird, the pigeon?'

Cranston laughed and gestured to where Doctor Mirabilis was now walking ahead of them.

'If you went to his little garret, you would find baskets of trained pigeons – you know, the type which carries messages. Every so often our friend here drugs one of them with nox vomica, a slow acting poison. The pigeon is released and takes up a stance nearby. The poor bird will remain immobile because of the effects of the poison. After a while it will drop down dead, and there you have his magic!' He laughed. 'Sometimes, of course, it does not work. Doctor Mirabilis here is always ready to run, fleet as a deer, fast as any hare!'

The learned physician, as if he knew his name was being mentioned, turned and gave a gap-toothed grin, waving at them to follow a little faster.

Athelstan now saw why Cranston had hired Mirabilis. Southwark was bad but this area around Whitefriars was worse. Even though it was still daylight, the alleyways and runnels were dark, closed off by the houses built on either side. A silent, evil place, becoming more ominous the deeper they went. The houses around them, built hundreds of years ago, now derelict and unkempt, huddled close together, blocking out the summer sky. Underfoot the track was dirty, caking their boots and sandals with ordure and mud. Most of the doorways were empty. Now and again a shadow would slip out but, seeing Cranston's long sword, retreat again. Mirabilis twisted and turned, Athelstan and Cranston finding it hard to keep up. Abruptly he stopped and indicated an alleyway, a long, dark passage ahead.

'Piper Alley,' he whispered. 'Goodbye, Sir!'

And, before Cranston could object, Doctor Mirabilis slipped up another alleyway and disappeared out of sight.

Athelstan and Cranston walked cautiously down Piper Alley. The houses on either side were shuttered and closed. At last they came to one fitting Doctor Mirabilis's description of Simon Foreman's house. It had a huge, battered sign at the end of a long ash pole.

Nightshade House was separated from the street by a flagged courtyard, the general approach defended by iron railings. Even in daylight it had a sombre, suspicious air as if it wished to slink back from the adjoining houses. More like a prison than a private residence, the windows were grated and the huge door barred and bound with iron bands. There was no answer to Cranston's knock, so he banged again. Behind them a dog howled and a door opened and shut. Looking down towards the mouth of the street, they saw shadows gathering. Again Cranston knocked. Athelstan joined him, hammering on the door with his fist. There was a sound of soft footsteps, of chains being loosened and bolts drawn back. The door was swung open by an unprepossessing man of middle stature, creamy- faced, and merry-eyed. He constantly scratched the bald dome of his head. Mirabilis looked like a magician, Foreman had the appearance of some village parson in his dark fustian jacket, hose and soft felt slippers. Like a host in some cheerful tavern, he told them to tether their horses and ushered them in, asking them to sit at the table and wait while he finished his business in his own secret chamber. They sat and glanced around. The room was surprisingly neat, tidy and well kept. A fire burned merrily in the hearth. Around the room were tables and chairs, some covered with quilted cushions, and on the walls shelves of jars which were neatly labelled. Athelstan studied the jars, dismissing them as nothing but mild cures for ague, aches and pains. They contained herbs such as hyssop, crushed sycamore leaves, moss – nothing that could not be bought at any apothecary's throughout the length and breadth of the city. At last Foreman came back, pulling up a chair beside them like some benevolent uncle ready to listen to a story or tell a merry tale.

'Well, sirs, who are you?'

'Sir John Cranston, coroner, and my clerk, Brother Athelstan.'

The man smiled with his lips but his eyes became hard and watchful.

'You wish to purchase something?'

'Yes, red arsenic and belladonna. You do sell them?'

The transformation in Foreman was marvellous to behold. The merry mask slipped, his eyes became more vigilant. He straightened in his chair, looking nervously over his shoulder. Athelstan sensed that, if he had known who they were before he answered the door, he would never have let them inside, or else would have taken measures to hide whatever he had in the house.

'Well, sir?' Cranston asked. 'Do you have these poisons?'

Foreman shook his head, his eyes never leaving the coroner's.

'Sir, I am an apothecary. If you want a cure for the rheum in your knee, an ache in your head, or your stomach is churned up by bad humours, I can do it. But bella- d›nna and red arsenic are deadly poisons.' He let out a deep s.gh. 'Very few people sell them. They are costly and highly dangerous in the hands of those who might use them for the destruction of life.'

Cranston smiled and leaned closer, his face a few inches from that of the apothecary.

'Now, Master Foreman, I am going to begin again. You do sell red arsenic, nightshade, belladonna, and other deadly potions to those who are prepared to pay. Look,' he lied, 'I have in my wallet a warrant from the Chief Justice and I shall stay here whilst my clerk hurries back to the city and brings men from the under sheriff to search this house. If one grain of poison, red arsenic, white arsenic, the juice of the poppy or any other damnable philtre is here, then you will answer for it, not at the Guildhall but before King's Bench! Come, surely somewhere in this house there are records, memoranda of what you sell?'

The apothecary's face paled and beads of sweat broke out on his brow.

'There would be many,' the fellow whispered, "who would curse you, Cranston, for dragging me into court! I have powerful friends.' His eyes flickered towards Athelstan. 'Abbots, archdeacons, priests. Men only too willing to defend me and keep my secrets – and theirs – hidden from the light the law!'

'Good!' Cranston answered. 'Now we understand each other, Master Foreman. I have no desire to stop your evil trade in whatever you sell, buy and plot, or to search out your secrets, though one day perhaps I will.' He stared up at the shelves above him. 'What I want now is to know who in the last month has been here to buy arsenic and belladonna? Surely you recognise this?' He took out the small stoppered jar of poison and Foreman's eyes rounded in surprise. 'This is yours, sir,' Cranston probed gently. 'Look, on your shelves, there are similar ones. Who in the last few weeks purchased this poison?'