The glasshouse on the Te Puna road at Pokeno is a thousand square metres in four bays, and the glass is four millimetres and forty years old, and the pipes under the floor are a hundred millimetres of cast iron laid three hundred apart in a slab poured in 1985. If the water in those pipes stops moving the floor goes cold, and if the floor goes cold the glass sweats, and if the glass sweats there is water on the plants. Tilly Ngata was sixteen and she was the one who wrote the numbers down.

The book was a hardback ledger on the boiler house shelf, ruled in five columns. Date, time, return, pump, slab. Two readings a day, six in the morning and six at night, kept in that book since 2009. Hemi Ngata wrote most of it. He is Tilly's uncle, and he is forty-four, and he has had a bad back since the twelfth of May. The day he stopped he put the book on the table and said the six o'clock reading was hers now. He did not say the other thing, which is that the book is signed by the operator, and an operator of a boiler that size has to hold a ticket.

Here is what the three numbers meant, and Tilly did not see it until the seventh of July. The return was the temperature of the water coming back into the boiler. The boiler fires until that water is sixty degrees and then it stops, and that sixty is a setting. A thermometer is a measurement. A setting is not a measurement, and a setting cannot go anywhere, so the return column said sixty every morning of her life and would have said sixty if the house had been made of ice. The pump column was a dial, and the dial was also a setting, and her uncle had walked it from seventy up to ninety-five between May and June and wrote the numbers down as though they were readings.

The fire went to a hundred per cent on the cold nights, which everybody in that house had read as a sign that the heating was working. The slab was the only column that was a measurement. It came off a long-stem probe, and the book said to push the stem into the trench at the two-inch lip and read it.

Condensation is arithmetic. The air in that house holds water, and the temperature you have to cool it to before the water comes out of it is the dew point, and the dew point is always under the temperature of the air. Hemi had a wet bulb on the boiler house wall, a glass tube with a muslin sock on it, and a psychrometer chart on the door printed in 1974. On the morning of the sixth of July the dry bulb in bay two read fifteen point four and the wet bulb read fourteen point two, which the chart puts at about seventy-eight per cent, and the dew point at seventy-eight per cent is a shade under twelve. The glass in that house was thirteen point four.

The bar over bay three was eleven, because the bars are aluminium and run from the gutter outside to the ridge, and they are the coldest thing in that building, and no amount of hot water under the floor changes that. The grower was Grant Ledgerwood. Tilly had watched the bars over bay three sweat since the middle of June, and on the twenty-ninth of June there was a brown fur on the stalks where the trusses meet, the grey fur the men in the packing shed call tobacco. He came into bay three on the fourth of July without his coat off. “How long has the third bay been cold.” And Tilly said, “Since May.” And Grant said, “Since May is a thing you tell me in June.”

The slab column in the book ran like this. 14 May, eight point one. 21 May, eight point zero. 28 May, seven point six. 4 June, six point four. 11 June, five point one. 18 June, four point six. 2 July, four two. And the other three bays, when she put the stem into them, read twenty-two point four, twenty-two point one and twenty-two point six. That is eighteen degrees across one floor. A floor at twenty-two is doing the job it was laid to do.

A floor at four is taking heat out of the room, and the only thing in that bay that puts heat in is water in the pipes, and water that has not moved since April is the temperature of the trench it is lying in. The probe hung off the pipe in the trench in bay three and had done since before she started, so the numbers in that column were true numbers for the true place, and they had been falling for seven weeks in her own handwriting, and nobody had read them, because everybody had decided that was the man's back.

She told Grant on the fifth, in the boiler house, with the book open on the bench. He put his finger on the twenty-second of May. “That is the third bay probe. It has been the third bay probe since your uncle started. It is the cold end of the house. It has always been the cold end of the house.” And she said, “The cold end is not four two.” And Grant said, “The house is fifteen degrees and the book says sixty at the return, and it has said sixty every morning of your life. Which of the two numbers in that book would you like me to believe.”

So she went and looked at the pipes. The four returns come through the wall of the boiler house four inches above the floor, one for each bay, a gate valve on each. She had the clip thermometer out of her coat, the round white dial with the black needle, and she clipped it on the first return and it read fifty-nine point four, and the second read fifty-nine point one, and the third read fifty-eight point eight, and the fourth read nineteen point six.

She stood there a while. Then she got the wet bulb and held it near the fourth pipe and it read thirteen, and the pipes either side of it were too hot to hold a hand on for a count of three. Then she put the stem in the trench under bay one and it came up at twenty-two point four, and then bay three, and it came up at four point two, which was the number in the book.

The trench in bay three had eighteen inches of water in it, and the valve on the feed to that bay was a gate valve the size of a fist with a long handle, and the handle was not on the valve. The handle had fallen out of it after twenty years, and somebody had put a loop of fencing wire through the wheel and pulled it up tight, and it had rusted where it crossed itself so it could not be unwound, and it was not fencing wire but soft copper out of the troughing, twisted on by somebody in a hurry.

The gutter over bay three had leaked on the ninth of April and was back on by the second of May. The service book in the boiler house had one line for the eleventh of April in the hand of Ra Pascoe, and it said bay three floor circuit isolated for gutter repair, valve to remain shut, and under it in her uncle's writing, P says he will ring when the gutter is done. There was nothing in the book after that. Hemi's log for the twelfth of April said third bay floor water cold no flow, and his log for the twelfth of May said somebody has to look at that valve.

Opening the valve was the easy half. Getting the water out of the bay first was not. There are six and a half thousand litres in that one bay's floor, and the trench drains to a sump, and the sump was blocked with coir and tomato roots, and to drain bay three they had to crack the sump open with a bar, and the water came up through the slab and out across the bay, and there were four hundred tomato plants in grow bags standing in it. Grant would not have that, and he said the third bay was already grey from one end of the rows to the other and there was not a kilo coming out of it, so what was the water for.

On the sixth of July the boiler was at a hundred per cent, the dew point in that bay was eleven point seven, the floor under it was four point two, and the bar over the door was eleven, which is under the dew point, and the water came off the bar all night and stood in the trough. At ten past six Tilly Ngata wrote 4.2 in the slab column, the coldest number that had ever been in that book. The third bay was written off on the eighth of July. Four hundred plants, the botrytis in the fruit on the second truss, and the smell could be smelled from the path.

The contract was seven thousand kilos a week and the house was picking six, so Grant bought a week and a half from a grower in Māngere at eleven cents a kilo more than his own, and the packhouse man took it without saying anything, which is the part that costs.

Then Grant said, “Do it your way, then. Ra comes on Thursday and you go with him.” The bar went down into the sump and the six and a half thousand litres came up through the slab and across the bay, and Tilly and Ra Pascoe ran a hose to the tanker. Ra cut the copper off the wheel with a grinder and got the handle out of his bag, and the circuit filled and was bled at the far end of the bay for an hour and a half, because the pump holds air. The pump went back to seventy per cent, which is where her uncle had it in April. The book said sixty at the return, because sixty is the setting. The bill was eleven thousand dollars. Tanker, Ra's day, the bar, the crushed stone, and one night of no heating on the coldest night of that winter so far. Grant wrote the number on the board in the packing shed and nobody argued with him about it.

Bay three came back over two days, and by the eleventh the floor under that bay was at twenty-one, and by the night of the fourteenth it was at twenty-one point eight with the air at fifteen point four, which is six point four degrees, and the dew point was eleven point seven, and the glass was thirteen point four, and the bar over the door was eleven point one.

The bar is the only thing in that house she could not account for. It is the coldest thing in the building, and the only thing that decides whether it is wet is whether it is under the dew point, and on a clear night in a house with a crop in it, it is. She wrote 11.1 in the slab column on the fourteenth of July and then, on the same line, in pencil, she wrote a question mark, and she did not cross it out, and she has not been able to make it fit since.

The last page of the boiler book that winter is the fourteenth of July, and in the margin opposite it, where the other pages had the time and the initial, it says T. Ngata. The twelfth of October is the inspection, and the bar over the door of bay three was wet again at ten past six.