The loud ring and the smell of cooking brought Maura to her senses. The screen of her phone illuminated the now dark room and burned her eyes.

Pulling herself into a sitting position, she stretched her arms up and out before answering the call.

"Dr Isles"

"Oh thank God you're okay." Nina's relieved voice sang through the receiver. The woman hadn't been working for Boston Police Department all that long, but she was an invaluable member of the team and, now engaged to Jane's brother Frankie, she was part of that warm, Rizzoli family much in the same way as Maura was.

"I'm fine. Don't worry. It's… I'm just helping out a friend. But I'd like to know if you've found anything."

Nina sighed. "I'm glad you're alright. So. Harriet Catherine Morgan. Born, as you said, May 1977 in Boston to Barbara and Charles Morgan. Barbara remarried Bill Hunter in 1985 and they have one son, born in 1990."

"Joshua. Yes, I know."

"Her financials are clean, her academic records at both BCU and Oxford are perfect. There's nothing on this girl. The only thing I could find was that her name came up in a report on an on-going murder investigation. She was a person of interest, but not anymore. Is… is that why you're there?"

"Yes. She… her friend was killed. I was the first person she thought to call. And, of course, France isn't so far away so now I'm here."

"Maura" Nina's tone changed.

"I'm fine. Any sign of trouble and you'll be the first person I call. Okay?"

"No. I'll be the second person you call. If you're in any trouble, if anything at all seems suspicious, you call Jane. Boston police have no jurisdiction, but if a US national is involved in something, the FBI do have a right to know and they can step in if they need to. So call Jane."

"I will. I… I will if I need to. Nina?"

"Yeah?"

"Please don't tell her what's going on. She'll only worry, and then she'll be here and…"

"I get it. She's full on. She'll worry and she'll get all overprotective and you'll never finish that novel."

Maura tried her best not to sigh at Nina's words. "Something like that. Just… promise me?"

"Okay. But you keep yourself out of trouble, you hear?"

"I will. Give everyone my love."

"I will. Be safe."

As Maura ended the call, she heard a soft knock on her bedroom door.

"Come in" she said.

Harriet peered around the door, smiling at Maura. "I've made us some dinner. It's ready when you are- if you want to shower first, it can wait. I'm just going to throw on some comfier clothes- I managed to get chicken stock all over my shirt."

Maura laughed at the sight of the grown woman's stained shirt. "You always were such a messy cook!"

After a quick shower, Maura changed into a pair of black leggings and an oversized BPD t-shirt that she was sure had found its way into her case by accident. With her hair piled on top of her head and her black-rimmed glasses perched on her nose, she looked twenty years younger.

"Now that's the Maura I remember! I mean, you always knew how to dress well but casual just… suits you."

Maura smiled warmly, taking a seat opposite her friend at the small two-person table in the kitchen.

"Now, I should have checked earlier, but I forgot. You do still eat meat, don't you?" Maura nodded.

"Excellent."

With a steaming bowl of chicken and mushroom risotto in front of her, it dawned on Maura how long it had been since she had eaten a proper meal.

"This is gorgeous" she complimented Harriet after the first mouthful. Harriet nodded back, smiling.

"Thanks. I… I haven't felt up to cooking since I got the call. But having you here it… I feel so much more relaxed. It's like a weight has been lifted knowing I can share what's going on with someone who understands."

Smiling at her friend, Maura took another mouthful and sighed at the comforting warmth.

"You know, we really should talk about what's happening. I don't know much about your friend at all. Plus, it might help if you talk about it. Bottling things up is a dangerous habit. So, tell me about Rachel."

The sound of her friend's name seemed to stall Harriet. Blinking slowly, she got up and wandered to the fridge. Pulling out a chilled, green glass bottle, she poured a healthy measure of the pale liquid into a waiting glass and drank it down. Pouring herself another, she gestured the bottle in Maura's direction.

"Please." Maura nodded.

Sat back at the table, wine in front of both of their places, Harriet shook out her hands nervously.

"Where to start? Well. Rachel and I met at a Florence Nightingale celebration event at the British Museum in London. We were the only two Americans there, and once we got talking we realised we were both from BCU. She was still there- I think she was just about to graduate and they'd already offered her a research post, but she wasn't sold on the idea. She wanted more freedom. She was so… enthusiastic and I could see so much potential. So I spoke to another professor in the faculty and the bursar and, before the end of the week, I'd offered her a doctoral scholarship she couldn't refuse. She started at Oxford the following September.

Her thesis was on wartime codebreaking and how the Bletchley Park system changed society's view of women of high intelligence. I found it all absolutely fascinating. Well, so did a lot of other people. Before she'd finalised her thesis, she was being approached about book deals. The night she was… the night she died she was in Bedford. She was due to speak at a 1940's festival at Bletchley Park the next day. She… she contacted me to say she had a few clear days in her calendar after the festival and that she would love to meet for coffee. I called early and left a message to wish her luck, but she… she was already dead."

Maura reached over to stroke Harriet's hand as the woman took a shuddering breath.

"When the police called, they came to the office. They… they told me then and there that she was dead and that I was the first person they had found with a definite connection to her. She was in the foster system most of her life, in a group home, and her boyfriend left her last year. So she had nobody left. Nobody they could find."

"Why did she write your name?" Maura asked after a pause, unsure if quizzing her fragile friend would give her the answers she needed.

"I have no idea. I… I was her friend, but I have no idea why she would name me in that way."

"Was it just your name? Or was there more to the message?" Maura asked, using the calm interrogation techniques Jane had taught her when she first began working at BPD.

"Harriet Morgan. DEP RUP GUQ. The police were baffled. They asked so many questions."

"Do you have any idea what it means?"

Harriet shook her head. "None. That's what I told them. She… she liked codes, though. It was a huge part of her Bletchley work."

Maura pulled a piece of kitchen towel from the roll on the worktop and found a pen in a pot by the windowsill. "Say it again."

"DEP RUP GUQ"

Maura sat in silence for a moment. Harriet watched with intent curiosity as her friend's eyes scanned the letters over and over again.

"Erup… no. Pug… no. Dep… no. There's no word here. No anagram. Well, not in English."

"I love that you can do that. I'd have been here for hours." Harriet smiled. "And before you ask, she only spoke English and basic German. Enough to understand some elements of the German code from Bletchley but only with a translator app on her phone."

"Did Rachel's work involve the Enigma machine?" Maura asked after a pause. Harriet nodded.

"Not exclusively, but it was a huge part of the Bletchley operation. Why?"

"I… I just wonder if, maybe, we need to plug these letters in to the machine and see what comes back."

"Sounds good to me. We can do that tomorrow, if you like. It… it would help to keep my mind busy."

"Do you know where we can find one?" Maura asked, enjoying the fact that her friend seemed to have perked up.

"Bletchley Park."