It's Jack while he is chasing Carys during "Day One".
Jack groaned. It just wasn't his day – week – whatever. First Gwen, with her naïve eagerness reminding him painfully of Rose, now this alien controlled girl had his only reminder of the happiest times in his life. Only reminder, and only hope to get those times back again. Aiming his revolver at her, he snarled "Put the hand down! It's worthless to anyone but me!" it was half a command, half a desperate plea. He followed Carys to the door, telling her to give him the jar. He couldn't shoot, and she knew it. Jack could not and would not risk damaging the jar and its precious cargo.
Carys slipped through the doors. Jack cursed under his breath as he went around and raced up the steps. He burst in on Carys and Ianto with his gun drawn, ready for action. Jack brushed aside Ianto's offer of tackling her, and told him to open the door. He still wouldn't risk the jar. He was going to let her go. They could always find her again, and that hand was irreplaceable. He asked – begged – for the jar again as the girl went to the door.
Time seemed to freeze as Carys threw it behind the counter. Jack heard a roaring in his ears. Breathe! He needed to breathe! Jack was vaguely aware of his colleagues racing through the little shop, glancing at him as he knelt in the mess as they went after the sex-obsessed alien. Jack didn't care. He only felt relief now, crouched in the chards of broken glass and the fluids from the jar. The hand, the right Doctor's hand, was undamaged. He cradled it, just needing to hold it close.