But this evening, as the train left the city and took her through the rolling green Sussex countryside, Dee couldn’t focus on work. Her mind kept going back to the two little girls in the photo Emer had sent her. Opening Facebook, Dee clicked on Emer’s profile, but there were almost no posts. Not surprising, Dee supposed. Given Emer’s age – around thirty – she probably preferred other social media platforms.

Shutting down Facebook, Dee opened the Word document she’d created the previous day. Here, she’d made notes based on everything Emer had told her about her sister’s disappearance. Early on in her career, Dee had learned to always take notes, even for stories she might never write. Because you never knew when something you thought wasn’t a story might suddenly become one. Using these notes now, she opened her internet browser and typed in ‘Lahinch’ ‘1997’ and ‘Kitty Doran’. Then she sat back and started reading.

On the morning of Sunday 27 July 1997, Ursula Doran took her two daughters, Kitty and Emer, to the beach. Mrs Doran and her daughters were on holiday, staying at the Aberdeen Arms Hotel in the seaside town of Lahinch in Co. Clare. The girls’ father hadn’t come on holiday with the family. He’d stayed behind to work, and had planned to join them later.

Rather than go to the main beach, Mrs Doran took her daughters to a quieter stretch of beach, near the estuary where the river Inagh flowed into the sea. She claimed she’d chosen this location because it was less busy. What she didn’t realise, she said, was that the currents in the water here, where the river met the sea, were treacherous. Like many other holidaymakers before and since, she’d ignored the signs warning people not to swim and had decided this was the perfect place to spend the morning.

While Mrs Doran settled down to read a stack of magazines, her daughters started building sandcastles. At some point during the morning, the sisters had an argument and Kitty went for a walk, leaving Emer to play by herself. By the time Mrs Doran went looking for her daughter, she had disappeared.

Two days after Kitty disappeared, the shorts she’d been wearing were washed up on a beach six miles further along the coast. Despite an extensive search that went on for weeks, her body was never recovered. This wasn’t an unusual occurrence, apparently. The unpredictable nature of the currents made it a difficult – sometimes impossible – task to work out where a body might end up. There was no mention, in any of the articles that Dee read, about Emer’s potential sighting of her sister later that same evening.