"Thank you," she says, actually startled for a moment. It is a very ordinary name, but he - Alex - spoke like he meant it.

Part of her thinks: we're agents and spies. But the rest of her weighs up the cost of his name, and she smiles back.

She lowers herself back down onto the street, and touches her head against his shoulder as they start to walk again. She's used to his metal arm by now, but different circumstances breed a different awareness of how it feels under the heavy layers he's wearing.

"Do please tell me, Alex, that our bosses have let you ride the Metro before."