The Doctor, Rose, and Jack pop back to 21st-century Cardiff, so that Rose can meet up with Mickey, the TARDIS can refuel from the Cardiff rift, and mischief can generally be gotten into. Also, Jack isn't getting any from Rose, nor from the Doctor, which annoys him and amuses everyone else. (But the Doctor merrily flirts with him, which annoys him even more.) Still, our three travellers have bonded together in a way that really irritates Mickey, who is getting a little sick of all the inside jokes and all the flirting with each other that the three of them can cook up.