Anna smothered a smile and slipped out of the door, sure she could hear Paula’s sigh of relief as she closed it gently behind her.

Outside the sauna, she worked quickly, wrapping the towel around herself and picking up the poker in the box next to the door. She fed it through the door handle, careful not to let it clang as she released her grip. Then she padded soundlessly down the hallway, pausing at the lockers and grinning again as she spotted Paula’s bag on top. Obviously, the woman hadn’t bothered to stop in the spa reception and get a key.

She ducked into a changing room and pulled on her clothes. When she left, the spa area was still silent, still empty. She smiled to herself as she walked towards the exit, swiping Paula’s bag off the top of the locker as she passed. Once outside the door, she flipped the sign over to read Spa Closed, then made her way down the corridor.

Paula stared at the door long after the strange woman had left. Who sat in a sauna totally naked? And her body! Regretfully, Paula pinched the spare flesh on her own stomach. The woman must work out every day to look like that.

She picked up her towel and rubbed at her face, realising just how hot she was. Suddenly a walk on the open-air deck seemed like the perfect way to finish off her afternoon of indulgence. If she could track Tommy down, maybe he’d come with her, explore outside before they got dressed for dinner. She looked at her watch and saw she’d been in the sauna for almost an hour. No wonder she was sweating so profusely. And that hour was plenty of time for Tommy to have cooled off.

She stood, grabbed her towel and pushed at the door. It didn’t budge.

Frowning, she pushed it again, but it was stuck fast.

‘No,’ she whispered. Putting the whole side of her body against it, she shoved at it again and again. ‘No!’ She could hear the panic rising in her own voice.

Was it her imagination, or had the sauna suddenly got hotter? She let go of the handle, and lurched over to squint at the thermometer. It read 110 degrees – she knew it should be between 70 and 100 – and she had already been in there too long. What would happen if no one came to let her out? Would she pass out from heat exhaustion, or become dangerously dehydrated?

She slammed at the door again and banged on it with her fists. It was unlikely anybody else would come along soon; the rest of the passengers would be gearing up for the first night’s dinner and celebrations of the maiden voyage.

‘HELP!’ she shouted, grabbing at the handle again.