"I got a postcard!" Joe declared, calling out to Rebecca as he collected the post from the hall. "It's from Jean in Bath."

"Oh?" Rebecca replied from the kitchen, sitting opposite Lucas, who was refusing to eat. "Just one mouthful, please, sweetheart?"

However Lucas kept his mouth closed firmly, defiantly.

Joe entered the room, holding up the postcard.

"Says she's studying hard, the uniform is horrible but she's loving every minute."

"That's good," Rebecca agreed, unable to find enthusiasm.

"Are you okay?" He poured himself a glass of champagne to toast Jean with and came to stand next to Rebecca, looking into his son's face.

"Little changeling, aren't you, Lucas?" he joked, smiling at him.

"Please don't say that," Rebecca cut in, curtly, "it's not funny."

"Hey, sorry, I didn't realise—"

"It's fine," Rebecca held up her hands. "I just can't get him to eat."

"Well, I'd probably turn my nose up at it too if I was being served that." Joe nodded at the green mush.

"It's the best one, I read it in a magazine," Rebecca defended.

"Right, little man." Joe rolled up his sleeves and took up the spoon. "Daddy will have some and then Lucas will have some."

He swallowed some of the mush, immediately grimacing.

"Good stuff." He pulled a face. "Very green." He lifted the spoon with another scoop of the mush and held it towards Lucas. "Come on, Lukey, nice vegetables. Nice," Joe emphasised and to their surprise, Lucas took a taste.

"Why will he do it for you and not for me?" Rebecca whimpered, close to tears.

"Hey, it's okay," Joe held her close.

"I can't do anything right with him. He's always crying and I can't make him stop! I can't—"

"Baby, it's okay, I mean, we've got three, you're doing an amazing job."

"But I'm not." Rebecca sniffed. "I'm getting worse. I can't remember things, I can't keep track!"

Joe rubbed her arms comfortingly, nuzzling his nose in her soft hair. "I promise, okay, we'll work this out. I love you so much, so much. You don't need to worry about anything."

He looked to Lucas.

"Come on, buddy, smile for Mummy?"

Rebecca stood up sharply and walked away.

"Bec? Becca?" Joe called after her, but his attempt was futile.

"Just you and me then? Don't worry, Mummy's just a bit upset. We'll help her, won't we, Lukey?"

He lifted Lucas from his high chair and bounced him against his hip, looking thoughtful.

Rebecca came downstairs a little later than expected, looking weary, her eyes puffy.

Joe was sitting in the lounge, playing with Lucas, who was placing another block on top of a pile, his face fixed in concentration. His head turned sharply on sensing his mother and Joe leant back on his feet.

"You okay?" Joe asked her, slowly standing.

"How's he doing?" Rebecca queried.

"He's fine. We're playing blocks, aren't we, mate?" He ruffled Lucas's thick dark hair.

"I'm sorry, I ran away," Rebecca admitted, "just a bit overwrought."

"You're bringing up three kids, it's understandable. We can look at getting a Nanny if it's too much."

"It's not too much."

"Baby, you're exhausted." Joe put his hands on her shoulders. "It's okay to ask."

"Ask what? Because you think I'm incapable of looking after my own children?" Rebecca retorted.

"No, of course not. You're a great mum!"

"I don't need help, okay? I'm fine. The heat got to me today."

She crouched down beside Lucas, avoiding eye contact, and began to clear away the other toys. Joe looked on, helpless to say anything, wishing he knew what to do.

"I'm going to make some dinner," he said eventually.

"There's salmon in the fridge," Rebecca added in a monotone.

Joe nodded, walking out of the room.

Back in the lounge, Rebecca continued clearing things away, refusing to look at her son. It was such an odd thing that he should look so much like Joe's Auntie Zoe and Jean. But he had come out of her, she had seen him. Blonde with blue eyes. At the party.

Suddenly fear gripped her, what if someone had changed the baby? Maybe he was Jean's? She was a Nanny, it was the perfect opportunity.

But why would anyone want to steal her beautiful boy? This dark elfin creature couldn't be hers. No. He wasn't. She forced herself to look at him.

He was like Jean and Zoe, nothing like Rebecca or Joe or Joe's father and mother, the pictures she had seen of them confirmed that. So, who was this little changeling?

She tilted her head and Lucas followed her gaze, looking at her blankly with his dark eyes.

"Who are you?" she asked aloud.

Lucas merely stared, sneezing and promptly crying.

"No. No." Rebecca shook her head. "Don't cry. Don't cry. Please don't cry," she hissed, unable to bring herself to use his name.

Lucas clenched his fists, bawling.

"No, don't do this. Please don't," Rebecca begged, tears trailing her face. "Please."

However Lucas would not be contained and let rip, screaming.

"What's going on?" Joe ran across the hall at the sound of Lucas's wailing and found his wife sitting in tears opposite their obviously distressed son, doing nothing to comfort him.

"He's not ours," said Rebecca through her tears.

"What? Not our what?"

"He's not our son." Rebecca wiped tears away. "Not our boy."

"Becca..." Joe picked up Lucas to soothe him and then knelt down beside his wife. "What are you saying?"

"I think he was switched," Rebecca whispered. "You hear about it happening. Babies being switched in hospitals."

"That almost never happens, sweetheart," said Joe patiently. "And anyway, Lucas was born at home."

"Someone still could have switched him. Kim, maybe."

"Darling, you're just tired. Why would you think he isn't ours?"

"He doesn't look like us." Rebecca shook her head. "He looks nothing like Rachel or Seb."

"So? Not all siblings look alike."

"His hair's too dark to be ours."

"It's the same colour as Jean and Zoe's." Joe was losing patience now. "I must be a carrier for that gene."

"He's not ours. I can just feel it."

Joe sat back and stroked Lucas's face for a moment, before looking back at his wife. "What if we get a DNA test?"

"You mean you believe me?" She stared at him.

"No. I don't believe that Luke isn't our son, but I believe you believe it, and a DNA test is the only thing that'll put your mind at rest."

But DNA tests can lie, she thought. What if the doctors were in on it?

She didn't say this out loud, though, as Joe was still looking at her with concern and she knew he thought she was paranoid. "OK then. We'll get a test."

Joe nodded and reached out to stroke Rebecca's hair. "Get some rest, okay?"