This was the heart of it all. It was a two up, two down terraced house. The two down breathed out all the Badness, distributing the wealth of waste from the houses toilets, bathrooms, and collected rubbish. The two up breathed in fresh air, providing the house with the vital spark, the urge to live.
Knave lived in the downstairs flat. while Ivanova occupied the upstairs.

Every morning Knave went out with the rubbish. Took the Bin van to the Tip.
It was a landfill site that stretched for miles. The rubbish where he could
find his meals. He was a bagman, rummaging for half eaten tins of beans, bacon
rinds and unwanted cereal. A discovery was a breath of fresh air and he stuffed it into his black bin bag. You collected your meals here. You did
not eat them. First you had to make yourself sick to dissolve the rubbish and
then suck it up the black tube, always carried as a night stick against your
thigh. If you had been a fly on the wall you would have agreed with Knave.
It was the only way to consume. The food was expelled as air out of his backside.
Ivanova, flying above him now, made his air breathable with the rapid flapping of her wings. She remembered their Allotment Day. This was the occasion when Two Ups and TWo Downs found their mate. Each had to tell the other a secret and if the both were entertained then each was allotted the other.
Ivanova told Knave the following tale:
I will tell you my secret if you will tell me yours.
Once I flew and flew and flew over the Tip till I came to the edge of it. There I saw a Fluid that took part of the Tip away every time it washed over it. I was afraid that the Tip would disappear and nothing would be left but the Fluid.
In my fear I flew and flew and flew over the Fluid till it came to the point where it touched upon the Tip again. Here I saw the tip being put back by the Fluid. I was afraid that the Fluid would disappear and nothing would be left but the Tip.
I flew and flew and flew upwards so high I could see the part which took away the Tip and the part which gave it back. I could see the shape of the Tip always changing.
This is my secret

Knave told Ivanova:
You have told me your secret I will tell you mine
Once I shat upon the Tip and sat to watch it. After a few weeks a tiny green stalk appeared. I watched it a further week and it grew wings like yours. Then it began to rain acid and I feared the stalk would die. The wings began to yellow at the edges and I wanted to step on it.
Then the sun came out and shone and the yellowing went and the wings became green again. But the sun shone week after week and the wings began to turn brown and I wanted to step on it. Then the rain came again and it turned green again.
This is my secret.”
As they returned home, him below and her above, she remembered his sign of pleasure as an expelling out of his back side that her wings gladly purified.