It's Sereia's 18th birthday and she does something that she hasn't done for five years – she falls out of bed, waking her up ten minutes before her alarm is due to go off.

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Her duvet is wrapped around her when she falls and she assumes that this is why she can't move her legs. But when she disentangles herself from the duvet, she is in for a shock – her legs have disappeared and, in their place, she has grown a fish tail overnight.

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She's supposed to be meeting her friends for a night out – how's she going to explain that she's turned into a mermaid overnight?