“So,” said Alfie, toothbrush in hand, after he and Mrs Stokes had towelled themselves dry and let the bathwater out, “I think the key thing with this one is making it different, for once, from the morning version.”

“Hmm,” said Mrs Stokes. “How are we going to do that?”

“Can I help?”

They turned round. Standing there, in front of the bath, was Dolph.

“Are you OK to be out of the water?” said Alfie.

“Yes. I’m a mammal, not a fish. I don’t have gills. I breathe air just like you, only out of my blowhole.” Dolph bent his head and puffed towards Alfie, who felt the – slightly fishy – breath on his face. “As long as I keep my skin damp, I’m OK.”

“You see,” said Mrs Stokes to Alfie, “you’ve done your marine biology homework after all.”

“Yes, thanks, Dolph,” said Alfie. “But meanwhile: teeth?”

“Well, what I do is open my enormous mouth, let loads of little plankton swim inside and they feed on my teeth, cleaning them at the same time.”

“Right …” said Alfie.

“I’m sensing you don’t fancy that much, Alfie,” said Mrs Stokes.

“Really?” said Dolph. “I love it. They do a great job and it tickles. In a nice way.”

“Maybe this is different enough,” said Alfie, squeezing the toothpaste on to his brush.

“How do you mean?” said Mrs Stokes.

“Well, in the morning, I never have a talking dolphin in here when I’m cleaning my teeth.”

“Good point.”

So he started brushing his teeth. Just for good measure, Mrs Stokes and Dolph joined hands – well, hands and fins – and did a dance, an exact copy of one that Mrs Stokes had just watched on Strictly – the American Smooth – to the rhythm of his brush strokes. Just to make sure this teeth-clean was very different.