The hammer rang once. A spark jumped off the anvil and did not go out. It waited. They followed.

It happened at the bus stop on a hot Thursday in June, in less than a second.

Tara was sitting on the bench with her phone on her knee, reading over her history notes one last time before the exam. The bus came round the corner. She stood up too quickly. The phone slid off her knee, bounced once on the edge of the bench, and landed face down on the pavement with a small, flat, horrible click.

She knew before she turned it over.

The crack started in one corner and ran right across the screen, in a long jagged line, with smaller cracks branching out from it like a frozen river. The screen still worked. You could see the time, and her history notes, through a sort of spider's web. But when she swiped, a little piece of glass came away on her thumb.

She did the history exam with the phone switched off in her bag, and thought about it the whole time.

After the exam she took it to Mr Lee's repair shop, which was the small shop next to the launderette, with phones of every colour in the window and a sign that said CRACKED? WE FIX. Mr Lee looked at it under a lamp and turned it over in his hands, very gently, like a doctor.

"Screen only," he said. "The inside's fine. Lucky. I can do it by tomorrow. Ninety pounds."

Ninety pounds.

On the bus home, she opened her banking app. She had two pots in it. One was her everyday account, which had eleven pounds forty in it until Saturday's pay. The other was the deposit pot. She had put a hundred and twenty-seven pounds fifty in it on the first of every month since September, without missing once. It said DEPOSIT — £1,147.50. There was a little picture of a house next to it.

And at the top of the app, as if it had been listening, a bright blue banner had appeared.

Need a little extra? Borrow £90 now, instantly. Pay back £108 next month. Tap here.

She looked at the crack. She looked at the house. She felt a jolt of something that was mostly panic, and then, underneath it, the beginning of a very sensible-sounding plan.

"I was going to borrow it from the deposit," Tara said.

She was at the back table of the Whetstone café, with the cracked phone face up on the table in front of her like evidence. Danya was there, peering at the crack with great interest. Across from them sat Marcus, who kept envelopes for everything, labelled in thick marker pen, and who had a new one in his hand that said SUMMER.

"I was going to say it like this," said Tara. "Just this once. Ninety pounds out of the deposit pot, to fix the screen. Then next month I put a bit extra in, and nobody ever knows. It's my money. It's not like I'm spending it on anything silly. I need a phone. And I'm definitely not tapping the blue thing."

She already had her thumb over the button. Move £90 from DEPOSIT to Everyday.

It felt good. It felt like the grown-up answer. Quick, quiet, sorted.

Marcus looked at the app, and then at the phone, and then at her.

"Give every pound a job," said Marcus. "What's the money in that pot for?"

"The deposit," said Tara. "Obviously."

"And what's the ninety for?"

"The screen."

"So you've got a pound that's already got a job," said Marcus, "and you're going to make it do a second one. What happens to the first job?"

"It gets done next month," said Tara. "I'll put it back."

"With what?" said Marcus.

Tara opened her mouth. Then she shut it again.

"Says who it won't go back?" said Danya. "She always puts money in. She hasn't missed a month."

"Nobody says it won't," said Marcus. "But nobody's said where it will come from, either."

"How do we know she'll have an extra ninety next month?" Danya asked.

Nobody knew. That was the problem.

Marcus emptied his bag onto the table. It was mostly envelopes. BUS. LUNCH. BIRTHDAYS. ONE DAY. SUMMER. Each one had a little column of numbers written on the back in pencil.

"Write the plan before the money comes," said Marcus. "That's all envelopes are. A plan, with the money already in it. So let's look at your plan."

Tara got out the folded plan from her bag and flattened it on the table. Nine months of pencil. £127.50 a month, every month, for the deposit, underlined twice, at the top. Underneath, the other lines: gym — no, Sundays — keep, laptop — refurbished, presents — £40, headphones — £180 — mine, Easter — £120 max.

Marcus read it, line by line, slowly.

"This is a good plan," he said. "Really good. Nine payments. One thousand one hundred and forty-seven pounds fifty. You've nearly done it." He tapped the page. "But look. Every line has a job. The deposit. The headphones. Easter. There isn't a single line for this."

He put his finger on the cracked phone.

"There's no envelope for things you didn't know were going to happen," said Marcus. "So when one happens, it has to steal from an envelope that's already got a job. That's what you're about to do. And I'll put it back isn't a plan. It's a plan with no money in it."

"So what do I do?" said Tara. "The screen's still broken."

"How much do you actually need?" said Marcus. "That's my next question. But not for the screen. For the next one."

"What's the ONE DAY envelope?" said Danya, picking it up. It was fatter than the others, and softer, as if it had been opened and closed a great many times.

"That one," said Marcus, "is for one day, when something breaks." He took it back, a little protectively. "I started it in Year 9, after my bike tyre burst on the way to school and I had to walk for a fortnight because I'd spent everything on a game. Two pounds a week. It's not for anything. That's the point. It's for whatever it turns out to be."

"Have you ever used it?" said Tara.

"Four times," said Marcus. "A tyre. A phone charger. A school trip that nobody told us about until the Friday. And my sister's birthday, which I forgot, which is not really a surprise but felt like one." He turned it over. On the back, in pencil, was a long column of small numbers going in and a short column of bigger ones going out. "Every time, it was there. I didn't have to borrow, or take it from SUMMER, or ask Mum. I just opened it." He put it down on top of the others. "It's the most boring envelope I've got. It's also the one I'd keep if I could only keep one."

Tara looked at her folded plan again, with every line already spoken for.

Cyrus worked the till at the electronics shop on Saturdays and read the small print on every finance leaflet they handed out, mostly so that he could explain it to the customers. He had been reading the blue banner on Tara's phone upside down.

"What's the total you pay back?" said Cyrus.

"I'm not doing that one," said Tara. "I told Marcus."

"I know," said Cyrus. "But you should know why, not just that you shouldn't. Read the line under the big number."

Tara read it. Borrow £90 now. Pay back £108 next month.

"Add it up," said Cyrus. "You borrow ninety. You pay back a hundred and eight. So borrowing it costs eighteen pounds."

"Eighteen pounds isn't that much," said Tara.

"For one month," said Cyrus. "Eighteen pounds on ninety is a fifth. Twenty per cent. In a single month. If you borrowed like that every month for a year, it would be enormous." He shrugged. "Small payments, big total. It says instantly and a little extra in nice blue letters. Borrowing costs something, even when it says it doesn't. Especially then."

"So the deposit's cheaper," said Danya. "Borrowing from yourself is free."

"Free in money," said Cyrus. "Marcus is right that it isn't free in everything else. But it's a lot cheaper than the blue thing."

He turned the phone back the right way up.

"Twenty per cent a month," he said, "for not having a rainy-day pot."

Sofia kept every score of the school basketball team in a notebook and liked a long list of numbers more than almost anything. She had been listening, and she had her notebook out already.

"Look at the whole season, not one game," said Sofia. "This isn't one bad day. Write all twelve down first. Or nine, in your case. Every surprise you've had since September."

"There haven't been many," said Tara. "This is the first big one."

"Write them down anyway," said Sofia. "The small ones too. Anything you had to pay for that wasn't on the plan."

Tara thought. Then she started writing, slowly, on the back of the plan, remembering.

October: bakery apron, £15. She had forgotten that one completely until she wrote it.

November: lost bus pass, £24.

January: school trip to the museum, £12.

March: school shoes, because the old ones split, £30.

May: new calculator for the exam, because the old one stopped working, £19.

She looked at the list. Five lines. She had not thought of any of them as surprises at the time. Each one had just felt like a nuisance, and each one she had paid for out of whatever was in her everyday account, and then been a bit short that week.

Sofia added them up. "A hundred pounds," she said. "Exactly. In five months out of nine."

"That's only a hundred," said Tara.

"Over nine months," said Sofia. "Divide it by nine. That's about eleven pounds a month. Every month, on average, something you didn't plan for costs you about eleven pounds. Some months it's nothing. Some months it's thirty. This month it's ninety." She tapped the notebook. "Every team has a spread. A very bad day is usually followed by a more ordinary one. But there's always another bad day coming, somewhere. The average is only half the story."

"So surprises aren't really surprises," said Danya slowly.

"Each one's a surprise," said Sofia. "That there'll be one isn't."

"Let me listen first," Tara said.

She took the plan, with its nine months of pencil on the front and Sofia's list of five surprises on the back, and drew a line under everything. Under the line she wrote three things: what the deposit is for, what the screen costs, what the next surprise will cost.

The first was easy: the deposit, nearly done. The second was easy: £90, or £108 with the blue thing. The third she had to think about. About £11 a month, she wrote. Nobody knows which month.

Priyanka came in while she was writing, with a bag of revision cards and a milkshake. She read the plan over Tara's shoulder.

"I don't get it," said Priyanka. "It's all your money. All of it. The deposit pot's just a label in an app. If you move ninety pounds from one label to another, you've still got exactly the same amount of money. A pot is just a picture of a house." She shrugged. "Just use it."

That was true. It was exactly the same money. Tara could not argue with the arithmetic.

Then Mr Lee texted, because she had left her number.

Hi Tara, I can do it for £90 tomorrow morning. Honestly that's a fair price, the screen part alone is £60 for your model. If anyone quotes you less, check it's a real screen!

That was true too. She had looked. Ninety was fair.

Then her mum rang. Tara had sent her a photo of the crack from the bus.

"Oh, love," said her mum. "Look, let me lend it to you. Don't touch the deposit. Pay me back whenever. That's what family's for."

And Tara knew, because she lived in the same house, that June was tight for her mum too. The electricity bill had come on Monday. Her mum had read it standing up in the kitchen and then sat down.

"Can I say one thing?" said Tara, to the table, when she had put the phone down. "I think we missed someone. Me, in October. And November. And March. Every time, I just paid for it and was short for a week, and never noticed it was a pattern. I'm about to move away and pay my own bills. There'll be a lot more than five surprises."

Nobody said anything for a moment.

On the table in front of her was the cracked phone, with its spider's web, and the little shard of glass on a napkin. There was the banking app, with its blue banner, pay back £108, and the pot with the little house, £1,147.50. There were Marcus's envelopes, BUS, LUNCH, BIRTHDAYS, ONE DAY, and Cyrus's twenty per cent a month, and Sofia's notebook, about £11 a month, every month. There was Priyanka's milkshake, and Mr Lee's text, and her mum's voice saying that's what family's for.

And there was the folded plan, open on the table, with nine months of pencil on it, and a pencil lying across it, and a space at the bottom where a new line would go.

Tara picked up the pencil.

 

 

(Write the new line Tara pencils on her folded plan.)

 

The spark dimmed to a warm dot and settled back on the anvil. The Green was just the Green again.

Back on the Green

That afternoon Lan, who was seven, spent all her pocket money on stickers at the corner shop. On the way home her ice lolly fell on the pavement.

She asked Danya if she could borrow twenty pence for another one.

Danya gave her twenty pence. Then he asked her what she would do next time.

Lan thought about it. She said that next week she would keep one coin in her other pocket, the one with the zip, just in case something fell on the pavement.

She did, too. She kept it there for a whole month.

Afterword. The idea in this case is an emergency fund: a small pot of money kept only for things you did not plan for. Surprises feel rare because each one is different, but over a whole year they are not rare at all. Adding them up, as Tara does, often shows a steady average cost, which can be saved for in advance, a little each month. Without such a pot, a surprise has to be paid for by borrowing, which costs extra, or by taking money meant for something else, which quietly breaks the plan. Priyanka is right that money is the same wherever you keep it; the pot is a label. But labels are how plans work. You can practise giving every pound a job in LedgerQuest, and looking at a whole season instead of one game in InferForge.