Casey stared at her in bewilderment. ‘We can’t sleep while Dominic and Emily are . . . And Poppy . . .’

‘Just for a few hours,’ said Miranda. ‘You have to.’

‘I’ve got a couple of calls to make.’ Casey was edging towards the escalator. ‘At the very least, I’ve got to give Emily a reason why we didn’t turn up at Tilney Cottage. You go home.’

‘Who are Tartarus Energy anyway?’ Miranda called after her.

‘Bantham mentioned them by mistake.’ Casey turned back briefly. ‘They own the rights to drill oil in a big chunk of central Africa. But there is a rival company that claims to hold the same rights as well, because they were awarded by an early government. A mess. The MPs were due to make quiet representations to their president on behalf of Tartarus.’

‘Typical.’

‘Go home, Miranda,’ said Casey. ‘I won’t be long.’

As soon as she was at her desk, Casey pulled up the MPs’ register of interests. It was a huge list, regularly updated, of all the people or companies who had funded parliamentarians’ fact-finding trips or campaigns. It also showed some of the MPs’ own financial interests. In theory, an MP couldn’t own 20 per cent of a company and then stand up in the Commons to make long speeches about its brilliant products. In theory, an MP couldn’t be sent on a five-star junket to Antigua by a pharmaceutical company, and then vote for amendments that gave the company a huge tax break. In practice, loopholes had been found, time and time again.

Now, Casey read through the register carefully. She searched for the six MPs she had seen in Washington DC, hunting for the name of the company that had funded the trip.

‘Chrysos Finance,’ Casey read to herself a few minutes later. ‘Someone’s got a sense of humour, at least.’

She pulled up the threadbare information available for Chrysos Finance. Superficially, it was a small company offering wealth management for optimistic retirees. A basic website provided an address in the heart of the city, superimposed over glossy photographs of skyscrapers and smiling men grouped round a polished boardroom table. Just enough detail to avert the attention of a busy political correspondent. Deliberately mundane, thought Casey, and not even a phone number.

The Chrysos logo was a golden raindrop.

Zeus transformed into a shower of gold to seduce Danaë, Casey read in one of the books on Xavier’s desk.

Googling, Casey found that forty-seven other companies operated from the same office at Chrysos. Casey looked up Chrysos’s accountants. The same as Tartarus Energy. She sighed to herself.

Leaning back in her chair, she called Gabriel Bantham.

Bantham sounded furtive as he answered the phone.