What happened in Rose?
What's your personal canon on the few seconds the TARDIS disappeared at the end of Rose? Did the Doctor come right back? Or did the TARDIS send him right back? (She does know best.) Did he go off and have some adventures first? Did S2 Ten visit Nine and tell him to go back?
(Then S3 Ten would show up and tell him not to. Then S4 Ten would try and distract S3 Ten with some Snow Patrol and a blank journal for poetry writing. Meanwhile Specials Ten would go off and stalk Rose while Nine's back is turned...)