‘I understand. And I believe you, but even if you are a killer, you are hardly likely to admit it to me,’ Dr Abiola said.

‘I’m not a killer,’ Harri replied, flushing crimson.

‘Good, but that’s not my concern. What I am interested in is your track record prior to the event that led to your dismissal. You were a good detective, first in London, then up here, and, according to the people Nick knows in the Met, you had an excellent clearance rate.’

Dr Abiola walked through the open doorway. ‘Come,’ she urged gently. ‘Through here.’

The security guard at the desk eyed Harri the way people always did when they discovered why she’d been kicked off the force. She wanted to explain herself, but she knew it would do no good. So she shone her warmest, most innocent smile at the man, and followed Dr Abiola through the doorway. Nick came in behind them.

They entered another small antechamber that was separated from a larger room by a reinforced glass window that spanned the eighteen feet of the far wall. Another security door had been cut into the window, and was also surrounded by a vacuum seal. Beyond the window were rows of shelves that stored radioactive and toxic substances. At least that’s what the large, bright warning signs said.

‘It seems your instincts are still good,’ Dr Abiola said. ‘The government imposes strict controls on organizations authorized to use certain materials. We have safeguards . . .’ she trailed off. ‘Well, you can see the level of precautions we take.’

Harri looked around. They were in a vault at the heart of the building, and the materials room that lay beyond the reinforced glass divider was a vault within a vault. She couldn’t believe what she was hearing.

‘An inside job?’ she guessed.

A burglary would have been almost impossible, and the university would have noticed a break-in sooner.

‘Our safeguards were circumvented,’ Nick admitted. ‘Someone has stolen a small quantity of Cobalt 60. We’re conducting a full investigation, but it seems clear it was an insider.’

‘Cobalt 60 is used as a tracer in chemical reactions and for radiography. It is radioactive, and can cause lymphoma,’ Dr Abiola revealed.

‘Why are you telling me?’ Harri asked. ‘Surely this is a police matter?’

‘There is an official notification process,’ Dr Abiola replied.

‘But it will help the optics if we’re seen to have taken our own steps to recover the material,’ Nick added. ‘You’re a former police officer.’

‘And you already have an interest in the matter,’ Dr Abiola remarked. ‘You said you work privately now. If there is no conflict, we’d like to engage you as a private investigator to help us track down the missing cobalt.’

Harri didn’t know what to say. She’d never even considered becoming a private detective, but somehow she’d stumbled into her first case and secured her first client. She’d been obsessed with trying to prove her innocence and get her job back, but was she wasting her time? Was this her new life?