Castiel flew up to Mary's Heaven, standing at the side-lines where she wouldn't spot him. He watched as she danced around the space, surrounded by her memories of Dean at the different stages of his life she'd experienced, interacting with them all whilst beaming. She really was beautiful.

Dean's birth, and Mary sobbing joyously over her first child. Them being discharged from hospital and coming back to their house to set Dean up in his nursery, sending him to sleep and telling him, 'angels are watching over you.' Dean waking her up in the middle of the night for the first time.

Dean's first word, and Mary almost cried as she heard the word 'mom' come from his mouth.

Dean's first steps, as he walked towards her, away from John, and how Mary wished that it could have continued that way, away from what John would draw him and Sam into.

Dean's first day of day-care, when she walked him to school, and Dean's grip on her hand was tight from nerves, and he cried as he said goodbye to her that morning. Then when she returned to pick him up, and he ran into her arms and told her excitedly about his new friends and his new teacher, who he pointed out among the crowd.

Dean's first birthday party when he turned four years old, where he invited his friends round from day-care, who trashed the house and completely tired her and John out. Cuddling with Dean and singing 'Hey Jude' to him as he fell asleep in her arms that same evening.

And Sam's birth, and how excited Dean was when he found out he was going to be a big brother, and the awestruck look on his face as he looked at Sam resting in his mother's arms.

Dean helped her put Sam to bed, and cheered her up when she and John had had a dispute, and he made sure that Sam was looked after, which was all Kate ever wanted; for her two sons to be okay.

A hand touched Cas on his shoulder and he turned around. He faced Michael, and Castiel immediately looked down.

'What are you doing here, brother?'

'I…'

'Castiel, you cannot interfere with the Winchesters,' Michael said. 'We need them.'

'I know.'

'So you won't come here again, am I correct?'

'Yes.'

'Good.' Michael looked at Cas, seemed to notice his melancholy. 'I know we were instructed to love all humans, but you have to avoid them. We can't untangle the strings of destiny. We must accept them and move on.'

Castiel nodded, agreeing. Michael was right, of course, but Castiel couldn't help himself. He'd watched the Winchesters grow, of course he cared for them. He couldn't leave them, not when he knew what awful conditions they were in.

'Castiel,' Michael said before he left. 'If I hear of you being with either of them again after today, I'll remove both your memories and theirs. I am sorry, but this is the way it has to be.'

Castiel nodded again, but Michael had already left. He was glad Michael had done it himself; it would have felt worse if other angels knew. But he still felt hollowed out inside from the words.