‘Are you accusing me?’ howled Riggs, reddening.

‘Of course not,’ said Colbeck with a soothing smile. ‘You are evidently far too sensible to let such vital information slip. It must have been someone else. How many people knew?’

‘And where can we get in touch with them?’ added Leeming.

‘Let me see now,’ said Riggs, thinking hard and using his fingers to count. ‘Including me, there’d only be four of us — but I have complete faith in the other three. They’re all decent, reliable, upright men who’d never dare to be involved in anything like this.’

‘Would you care to put money on that?’ said Leeming.

‘I’m not a gambling man, Sergeant.’

‘It’s just as well because you’d certainly lose.’

Riggs fell back on pomposity. ‘My men are above suspicion.’

Colbeck was impassive. ‘Give us their names.’

Though she was pleased to see her father, Madeleine did find him a distraction while she was trying to paint. He kept coming up behind her to look at her latest railway scene and to offer unwanted advice. It was Colbeck who’d discovered her talent as an artist and encouraged her to develop it to the point where she was able to sell her work. There were other female artists in London but none specialised in pictures of locomotives in the way that Madeleine did. Landscapes and seascapes had no appeal for her and she lacked the eye for figurative painting, but there were few people who could bring a train so vividly to life on a canvas in the way that she did. It was a gift.

‘I’m surprised that he hasn’t been in touch with me,’ said Andrews, looking over her shoulder. He nudged her elbow. ‘You’ve got the wrong colour on that carriage, Maddy.’

‘I haven’t finished painting it yet.’

‘I thought the inspector would be banging on my door by now.’