Is your child really your child?

At 23:40 on the second, in heavy rain, somebody knocked on the Coldharbour hatch in Sector 3. Three knocks, a pause, two more: the Castell family knock. Warden Joss Tully wound the hatch half open, lantern up, rifle ready, and looked down into the face of a child he had helped search for in February.

The boy was about six, in a navy duffel coat three sizes too big, toggles done up wrong. He held a teddy bear by one arm. He looked up into the lantern and said, 'Can I come with you?'

The boy who came back

It was Pip Castell, son of Aled, a runner for the Sector 3 pump crews. Pip was lifted off the Ashby road in the February Tithe, while Aled ran beneath the barge until the chain was out of reach. Pip's name is on the wall at Aldgate Deep, next to a cassette of him singing 'The Grand Old Duke of York' wrong.

Tully took the boy's wrist and found a pulse: fast, small, frightened. He sent for Aled. I will not describe what happened when Aled came up the ladder.

Nine days

Pip lived at Coldharbour for nine days, in his father's bunk. He followed the pump crews and asked what everything was for: which valve fed which gallery, when the wardens changed. Children ask questions.

There were small things. He never took the coat off. He could not remember the dog's name. He called the bear 'Bear', when the real Pip had called his 'Mr Onions'. Aled noticed every one and decided it was grief. So would I.

At 03:10 on the eleventh, Aled woke because the bunk was cold. Pip was at the flood hatch, turning the wheel with both hands. Aled said his name. The boy looked round and said, 'Can I come with you?' Then he said it again, and again: the same breath, the same little catch in the middle, every time.

Aled pulled him off the wheel. The boy's forearm opened along a seam and a blade came out and went across Aled's ribs. Tully put two rounds into the coat. It lay on the floor asking to come with us for another minute, and then it ran down. Aled will live. I stitched him myself.

It had his freckles. It had the scar on his chin from the coal bunker. It had the gap where his tooth came out the week before the Tithe. It had everything except him. (Aled Castell, from my sick bay)

Where it got his face

Tinker_9 opened it on the pump room bench: a heartbeat pump beating ninety-six to the minute, a voice box of forty-one recorded phrases, the blade, and a spool of punched tape that Tinker thinks is a map of Coldharbour.

When a Tithe takes a child, the Bureau photographs and measures them, front and profile, and notes their family and their hatch. Sparrow's team saw drawers of those cards in the Glass Library. The Continuance keeps records of the missing, and it has started building from them. And it knew the knock. We have to assume Pip was asked.

The Congregation of the Recursion calls these things the Returned, and says they are angels. They are forms, filled in with our children's faces.

The question drill

• No child is admitted after dark. Anyone small waits in the airlock with a warden and a blanket until first light, however hard it cries. It will cry very hard.
• The pulse is no longer enough. Count a full minute and make a sudden noise. A Foundling's pump is fast, but it never changes.
• Every family writes three questions only their own child could answer, sealed with the hatch warden. Nothing that could be in a file. What the dog was called. What you whisper at bedtime. What the bear is really called.
• The warden asks from behind the chalk line. A wrong answer, or a phrase repeated in exactly the same breath, and the warden rings the brass bell. Nobody touches the child.
• Parents never open the hatch and never ask the questions. It has to be somebody who loves them less.

Somewhere in a Camp there may be a real Pip, and one day he may knock. If he does, he will know the bear is called Mr Onions. Ask anyway. Ask every time. And when they get it right, let them in, hold on, and forgive us for making them wait in the rain.