‘So that water –’ Kusanagi began.
‘– is your evidence, if there’s any left,’ Yukawa finished. ‘Even if finding trace particles of arsenous acid in the water filter isn’t enough to prove how she did it, proving that a deadly amount of arsenous acid had come out of that water filter on the day of Mr Mashiba’s death would probably be enough to prove my theory.’
‘I just told you, she used the water on her flowers.’
‘Then check the soil in the planters. I’m sure Spring-8 wouldn’t have any trouble finding arsenous acid if it’s in there. Though it might be difficult to prove that it came from the water she used at that time, at least it’s another piece of evidence.’
While he listened to Yukawa talk, something was tugging at the back of Kusanagi’s mind – something he couldn’t remember, something he’d forgotten that he even knew.
Suddenly it dislodged itself from the depths of his brain. Kusanagi gasped. He looked intently at Yukawa.
Yukawa stared back at him. ‘What? Is there something on my face?’
Kusanagi shook his head. ‘I need a favour. Actually, consider it a formal request from the Metropolitan Police Department’s Criminal Investigation Section to Imperial University’s Professor Manabu Yukawa.’
A hard look came over Yukawa’s face. He adjusted his glasses with the tip of a finger. ‘Go on.’
THIRTY-ONE
Utsumi stood in front of the door, looking at the now-familiar nameplate. Anne’s House. According to what Kusanagi had told her, it might as well have read ‘Ayane’s House’. After moving in, the widow had almost entirely cancelled classes.
Kusanagi, standing beside her, nodded. Utsumi pressed the doorbell.
A long interval passed without an answer. She was about to press the button again when a voice came over the intercom.
‘Yes?’
It was Ayane.
‘Hello, it’s Detective Utsumi from the Metropolitan Police.’ Utsumi leaned in close to the speaker, talking quietly so the neighbours would not overhear.
After a moment of silence, Ayane said, ‘Oh, Detective Utsumi. How can I help you?’
‘There’s something I need to ask, if it’s all right?’
Another pause. Utsumi could picture Ayane standing by the intercom inside, thinking.
‘I’ll be right there,’ she said at last.
Utsumi and Kusanagi exchanged glances. He swallowed.
They heard the sound of the door being unlocked. Ayane seemed surprised to see Kusanagi there as well.
Kusanagi lowered his head. ‘Sorry to drop in on you unexpectedly.’
‘I didn’t know you were here too, Detective Kusanagi,’ Ayane said with a smile. ‘Please, come in.’
‘Actually,’ Kusanagi said, ‘can you come with us to Meguro?’
The smile evaporated from Ayane’s face. ‘The Police Station?’
‘Yes. There are a number of things we’d like to go over with you. I’m afraid some of them are a bit delicate …’
Ayane stared at the detective. Utsumi followed her eyes, looking up at Kusanagi in profile. There was a look of sadness, even regret, in his face.
If she didn’t know why we were here before, she knows now, Utsumi thought.
‘I see,’ she said. A strangely gentle light came into her eyes. ‘I’d be happy to go along with you. But I need to get some things. Won’t you wait inside? It’s against my nature to leave guests lingering in the hallway.’
‘Certainly, if you don’t mind,’ Kusanagi replied.
She opened the door wider and invited them in.
The inside of the classroom was neat and tidy. She had obviously packed away some of the furniture she’d set up for her classes. Only the large table in the middle of the room remained exactly as it had been.
‘I see you haven’t hung up that tapestry yet,’ Kusanagi said, with a glance at the wall.
‘Surprisingly, I haven’t had the time.’
‘Really? You should definitely put it up. It’s such a nice pattern, like something from a picture book.’
She looked around at him, still smiling. ‘Thank you.’
Kusanagi’s eyes went out to the balcony. ‘I see you brought over your flowers.’
Utsumi glanced out at the balcony, too. She could see flowers in a variety of colours on the other side of the glass doors.
‘Just a couple of them, yes,’ Ayane answered. ‘I had a moving company help me bring over some stuff.’
‘That’s good. They look well watered.’ Kusanagi’s gaze lingered for a moment on the large watering can just inside the doors.
‘That watering can has really come in handy,’ Ayane said. ‘Thank you again.’
‘Glad it could be of service,’ Kusanagi said, looking back at her. ‘Please, don’t mind us. Do what you need to get ready.’
Ayane nodded and headed towards the next room; but before opening the door, she turned. ‘Did you find something?’
‘Excuse me?’
‘Did you find something out about the case? Some evidence, or a new lead? That’s why you’re bringing me in, isn’t it? More questions?’
Kusanagi took a sidelong glance at Utsumi before returning his gaze to Ayane. ‘Something like that, yes.’
‘What did you find? Or can you not tell me that until we’re at the station?’ Her tone was as light as if they were discussing the weather.
Kusanagi looked down at the floor for a moment in silence before saying, ‘We found out where the poison was. We had to run several tests, but it’s become very clear that it was inside the water filter in your kitchen.’
Utsumi was staring at Ayane’s face; barely a ripple passed across the woman’s benign expression. Her eyes as she looked towards Kusanagi were calm.
‘I see. In the filter,’ she echoed, no trace of surprise in her voice.
‘The problem was figuring out how the poison got into the filter. Based on evidence found at the scene, there was really only one method the killer could have used. And, based on this method, there’s only one possible suspect.’ Kusanagi stared at Ayane. ‘That’s why we need you to come with us.’
The faintest blush came to Ayane’s cheeks, but the smile remained upon her lips. ‘Do you have evidence that there was poison in the water filter?’
‘Arsenous acid was detected in the filter after thorough testing. However, that was insufficient proof, given that all indications were that the killer put the poison in the filter a whole year earlier. What we needed to prove was that the poison was present in sufficient quantities to be lethal on the day of Mr Mashiba’s death. In other words, we needed to prove that the water filter had not been used, washing out the poison inside, for an entire year.’
Utsumi noted that Ayane’s long eyelashes twitched at the precise moment Kusanagi said ‘an entire year’.
‘And did you prove it?’
‘I myself was flabbergasted when I first heard the theory that the killer had put the poison in place an entire year ago,’ Kusanagi said. ‘But you don’t seem surprised at all, Mrs Mashiba.’
‘I’m sorry if I’m not reacting. It’s just that everything you’re saying is so outlandish, I wouldn’t know where to begin.’
‘I see,’ Kusanagi said. He shot Utsumi a look. The junior detective reached into her handbag and pulled out a plastic bag.
The smile finally faded from Ayane’s face as she saw what was in the bag.
‘I’m sure you recognize this,’ Kusanagi said. ‘You opened holes in the bottom of this empty can to water your flowers.’
‘I thought you threw that out …’
‘I held onto it, actually. Didn’t even wash it,’ Kusanagi said, a hard look returning to his face. ‘You remember my friend Yukawa, the physicist? I had him examine this can in his lab. To make a long story short, he found arsenous acid. We were also able to determine that the acid had been in water from your filter. I also happen to have been present the last time this can was used – you were watering the flowers on your second-floor balcony. Hiromi Wakayama came and interrupted you halfway through. The can wasn’t used after that, because I bought a new watering can, and kept this one in my desk drawer.’