As Valjean calms down after the shocking terror of what he saw through the window, he sits with the sleeping Cosette at his side and has a realization. Hugo puts it this way:
He now clearly perceived the truth which was henceforth to be the centre of his life, namely, that while she was there, while he had her near him, he would need nothing except for her sake and fear nothing except on her account.
It’s while he is sitting there contemplating this that Valjean begins to notice the sound of a tinkling bell. Looking out beyond the shed he sees a man who appears to be walking along the garden, bending down and planting something. As this man moves the bell tingles. What kind of a man wears a bell like this? Why would he?
Valjean realizes that if he can see this man there is a chance the man will see him and makes haste to move Cosette and himself deeper into the shed behind some things that can hide them. He fears that if he is seen the man will cry out and Javert and his men will hear.
Protecting Cosette is his driving purpose now. Everything he does is for her. As they get hidden he notices that her little hands are freezing cold and he begins to fear that she will not survive the night. He determines that whatever the cost, whatever happens, she must be in a warm bed within the quarter of an hour. Valjean runs out of the shed to get help.
Our chapter leaves off here, so we’ll have to wait until tomorrow to see how this resolves.