As we passed down Cheapside we had to halt at the Great Cross to let a flock of sheep pass on their way to the Shambles. A long queue of water carriers was waiting with their baskets at the Great Conduit. I saw there was only a dribble of water from the fountain.

'If the springs north of London are drying up,' I observed, 'the City will be in trouble.'

'Ay,' Barak agreed. 'Normally we keep buckets of water to hand in summer in the Old Barge in case there's a fire. But there's not enough water.'

I looked at the buildings around me. Despite the rule they should be made of stone to avoid fires, many were wooden. The City was a damp place in winter – sometimes the smell of damp and mould in a poor dwelling was enough to make one retch – but summer was the dangerous time, when people feared hearing the warning shout of 'Fire' almost as much as the other summer terror, plague.

I jerked round at the sound of a high-pitched yell. A beggar girl, no more than ten and dressed only in the filthiest rags, had just been thrown out of a baker's shop. People stopped to look as she turned and banged on the door of the shop with tiny fists.

'You took my little brother! You made him into pies!'

Passers-by laughed. Sobbing, the girl slid down the door and crouched weeping at its foot. Someone laid a penny at her feet before hurrying on.

'What in God's name is that about?' I asked.

Barak grimaced. 'She's mazed. She used to beg round Walbrook and the Stocks Market with her young brother. Probably kicked out of a monastery almshouse. Her brother disappeared a few weeks ago and now she runs up to people screaming they've killed him. That's not the only shopkeeper she's accused. She's become a laughing stock.' He frowned. 'Poor creature.'

I shook my head. 'More beggars every year.'

'There go many of us if we're not careful,' he said. 'Come on, Sukey.

I looked at the girl, still crouched against the door, arms like sticks wrapped round her thin frame.

'Are you coming?' Barak asked.

I followed him down Friday Street, then down to Wolf's Lane. Even on this hot sunny day the narrow street had a sinister look, the overhanging top storeys cutting out much of the sun. Many houses leaned over at such an angle they looked as though they could collapse at any moment. Under the alchemist's sign I saw a crude repair had been made to the door with planks and nails. We dismounted and Barak knocked on the door. I brushed a layer of brown dust from my robe.

'Let's see what the pinched old crow has to say for herself this time,' Barak grunted.

'For Jesu's sake, she's just lost her husband.'

'Fat lot she cares. All she wants is to get her name on the deeds of this place.'

The door was opened by one of Cromwell's men. He bowed. 'Good day, Master Barak.'

'Good day, Smith. All quiet?'

'Yes, sir. We've had the bodies taken away.'

I wondered where. Did the earl have a place kept aside for inconvenient corpses?

The girl Susan appeared, looking composed now.

'Hello, Susan,' Barak said. He gave the girl a wink, making her blush. 'How's your mistress?'

'Better, sir.'

'We would talk with her again,' I said.

She curtseyed and led us in. I touched the old tapestry in the hall. It was heavy and smelled of dust. 'Where did your master get this?' I asked curiously. 'It's a fine piece of work. Very old.'

Susan gave it a look of distaste. 'It came from the mother superior's house at St Helen's nunnery, sir. Augmentations didn't want it – it was so faded it had no value. Great ugly thing, it flaps in the breeze and makes you jump.'

Susan took us into a parlour with another view of the strangely blackened yard, and went to fetch her mistress. It was a large room with fine oak beams, but the furniture was cheap and there was only a little poor silver on display in the cupboard. I wondered if the Gristwoods had gone beyond their means in buying this house. Michael would not have earned much as an Augmentations clerk and an alchemist's income, I guessed, could be uncertain.

Goodwife Gristwood came in. She wore the same cheap dress as yesterday, and her face was stiff with strain. She curtseyed to us perfunctorily.

'I'm afraid I have some more questions for you, Goodwife,' I said gently. 'I hear you have been to see Serjeant Marchamount.'

She gave me a fierce look. 'I have to look to my own future now. There's nobody else. I only told him Michael was dead. Which he is,' she added bitterly.

'Very well, but you must tell as few people as possible about what happened here. For now.'

She sighed. 'Very well.'

'And now I would ask you more about yesterday's events. Please, sit down.'

Reluctantly she took a chair. 'Did your husband and brother seem as normal when you and Susan left the house to shop?'

She looked at me wearily. 'Yes. We left before the markets opened and returned at noon. Michael hadn't gone to Augmentations yesterday – he went up to help his brother with one of his vile-smelling experiments. When we got back we saw the front door had been staved in and then those – those red footprints. Susan didn't want to come in, but I made her.' She hesitated. 'Somehow I knew there wasn't anybody here, not living.' Her tightly held features seemed to sag a little. 'We went upstairs and found them.'

I nodded. 'Is Susan your only servant?'

'She's all we could afford, silly lump though she is.'

'And none of the neighbours saw or heard anything?'

'The goodwife next door told your man she heard a great banging and clattering, but that was nothing unusual when his brother was at his work.'

'I would like to look at the workshop again. Do you feel able to come with me?' I recalled her terror at the notion the day before, but now she only shrugged apathetically.

'If you wish. They've taken them away. After you've seen it, can I get it cleared? If I'm to keep myself fed, I'll have to let it out.'

'Very well.'

She led me up the twisting staircase, still complaining about the need to let the room and how she had no money coming in now. Barak followed; behind her back he worked his mouth in a silent gobble in imitation of her. I gave him a stern look.

At the top of the stairs she fell silent. The door still hung off its hinges. I looked at the other doors leading off the corridor. 'What are these?' I asked.

'Our bedroom, my brother-in-law's, and that third one is where Samuel kept his rubbish.'

'Samuel?'

She grimaced. 'Sepultus. Samuel was his real name, his Christian name. Sepultus,' she said again, with mocking emphasis.

I went to the door she had indicated and threw it open. I had wondered if I might find the Greek Fire apparatus in there, but there was nothing but a jumble of broken chairs, bottles, cracked flasks and, staring up from a corner, a large toad preserved in a vinegar bottle. Barak peered in over my shoulder. I picked up an enormous, curved horn that lay on a cloth. Little pieces had been cut out of it.

'What in heaven's name is this?'

Goodwife Gristwood snorted again. 'A unicorn's horn, so Samuel said. He'd bring it out to impress people, powder up bits of it in his messes. I'll be reduced to boiling it for soup if I can't let some rooms.'

I closed the door and looked around the hall with its bare boards, its dried-up old rushes in the corner and the big crack in the wall. Goodwife Gristwood followed my gaze. 'Yes, the house is falling down. This whole street's built on Thames mud. It's drying out in this hot weather. Creaks all the time, makes me jump. Maybe the whole place will fall on my head and that'll be an end to all my problems.'

Barak raised his eyebrows to the ceiling. I coughed. 'Shall we go into the workshop?'

The bodies had gone but the floor was still covered with blood, its faint tang mixed with the sulphurous stink. Goodwife Gristwood looked at the spray of blood on the wall and went pale.