Gillard nodded. ‘Someone going to this trouble is not going to leave their dabs on the phone, are they?’

‘Well, the impostor girl wasn’t wearing gloves.’

‘True, but we’ve never seen her handling the phone.’

‘Someone was.’

‘Rob, there was an incredible level of preparation for this. That’s why I am now much more worried about the young lady.’

The Royal College of Music allocated Gillard a practice room for him to interview the other three members of the Lysander String Quartet. The large airy chamber had a high window which illuminated a beautiful old harpsichord as its centrepiece. But what the detective wanted from them required their eyes rather than their ears. Do you recognise this woman? That was the simple question he put to them. Karen Ellsworth, Ignacio Vacelar and Teus Zukowski, all in their twenties, sat together at a couple of folding tables, watching CCTV footage that the detective played on his laptop. The two male musicians looked up as soon as they saw the woman walking across the rainy car park at Clandon railway station. ‘That’s her,’ said Ignacio, a slightly built Spaniard with a morose expression.

‘Are you sure?’ Gillard asked.

‘Well, the hat, the coat and scarf are hers—’ Teus said.

‘They are, but this woman is slimmer, maybe younger than Beatrice,’ said Karen.

The three musicians then discussed elements of their friend’s hair and clothing, without coming to a firm conclusion. Gillard switched to the footage on the train, which was a little clearer because the angle was lower. He froze at a frame in which part of the woman’s cheek and eye could briefly be seen.

‘My God,’ Teus said. ‘It is someone else.’

Ignacio nodded his agreement. ‘She’s stolen Beatrice’s Politi.’

‘Her what?’ Gillard asked.

‘Her violin. It’s a 1932 Enrico Politi, made in Italy, worth many thousands. I recognise the case. This woman is swinging it about like it’s a cheap handbag. See, there! She just dumped it on the seat next to her.’ He shook his head as if this was the biggest part of the crime.

The other two nodded their agreement. ‘We do not know who this woman is.’ Karen pointed accusingly at the screen. ‘But she is not our Beatrice, and she is not a musician.’

Only then did Gillard tell them that Beatrice’s own father had agreed with their conclusion. The detective fast-forwarded through most of the rest of the CCTV footage, showing them a few salient moments of her movement through the carriage and ending with her departure from Earlsfield station.

‘Anything else you can tell me about her?’ Gillard asked. ‘I mean, are you sure none of you have seen this woman before?’

‘It’s difficult to tell,’ Ignacio said. ‘But no one at the college comes to mind.’ He looked to his colleagues for confirmation, and they nodded.

The detective spotted Teus feeling for Karen’s hand beneath the table, and giving it a squeeze. They exchanged wan smiles. Emotional preparation for bad news.