Will knows when Magnus is up to something or hiding something she doesn't want him to know. He knows it because he knows her, and because he's seen it, and he just knows. She's been away a lot--and it's not like he expects her to spend every waking moment with him, that's ridiculous, but this is just weird--and he's not sure what to think about it.

So when a patient cancels an afternoon appointment, he decides to go home early and maybe if Magnus is home, they can talk.

He comes in silently, in case Greg's asleep, and he hears Magnus singing. To the baby, he guesses, and after a moment he can tell he's right; Magnus is singing to Greg in a low voice. He stands there listening for a moment, remembering, because that act of a mother singing to her child gives him a lot of feelings, and then he hears, I'm sorry I've not been around, little one. Mummy's just had so many things to think about this week. It's nothing to do with you, I promise.

Will's not sure what to make of that.

So he backs away and goes to sit in the front room so he doesn't wake Greg; it's time for his nap and he knows Magnus is putting him down for it.