In all their school years no one had ever been asked to stay with Camilla, and Sarah had accepted the invitation with both alacrity and curiosity. But the sight of Piet and Camilla in the moonlight had almost severed their friendship. The following morning’s ride had been agony as she tried to behave cheerfully, to talk casually to Piet, as though nothing was the matter. All through the long, ruined day she struggled to conceal her pain and hostility. Back at school she had nursed her sense of betrayal, as she waited for Camilla to bring up the incident and offer some explanation. But none had been forthcoming. Camilla seemed not to have noticed her distant manner, and although there were moments when her anger boiled, Sarah was unwilling to confront her outright. She tried telling herself that Piet had never thought of her except as another kid sister. But this only served to exacerbate her jealousy. Then exams began and she blocked out everything else, spending every spare moment with her books, until one evening she was unable to find her biology notes.

‘I borrowed them yesterday,’ Camilla said. ‘I knew you wouldn’t mind.’

It was the pin taken out of the grenade and Sarah’s anger exploded. ‘I do bloody mind,’ she shouted. ‘You seem to think you can take anything you want and never bother to ask, because you’re posing as my friend. But you’re not my friend, never mind my sister, and when we get out of here I don’t want to see you again. Ever.’

Camilla’s expression was one of utter bewilderment and she opened her mouth to protest, but Sarah was in full spate and all her pent-up misery poured out. Camilla tried to apologise, promising that she had not initiated the incident, infuriating Sarah even further.

‘I don’t care who bloody started it,’ she said furiously. ‘You knew how I felt about Piet. Now stay away from me. I just want to finish my exams and go home.’

Camilla sat down, white and shocked, with no sign of her usual composure. ‘You’re coming to Nairobi,’ she said. ‘You’re coming to stay with me. It’s all arranged.’

She began to weep, suddenly and uncontrollably, and Sarah turned in astonishment. She had never seen Camilla cry. No one had. Her body shook and she bent forward, her face hidden in her hands, pleading between the sobbing.

‘Please, Sarah. Please. You must come with me. I can’t go home alone. You can’t turn your back on me, Sarah, please. I need you to come to Nairobi. You and Hannah are all I have, and now that school is finishing we have to stay together. We have to. We promised.’