[Dave]

Originally Posted by Dr.Jackson

It has been said that Tim (the boy) was partly psychic, which is possibly why the watch called out to him. On holding the watch and bumping in to Martha, he was able to see through the disguise and the fact that she came from a different time - the watch just amplified his ability. We were shown the actual version of events, interposed with his perception, given his latent 'Doctorness' (DT said in Confidential that there was always supposed to be something of the Doctor about the boy).

Originally Posted by HappyHippo

I think he was the Doctor, when he held the watch - in some way - so he was 'seeing' Martha through the doctor's eyes. Maybe before the first episode, as the Doc did mention he'd been around for a couple of days, trying to trace the whatchamacallits the Rhinos had set up? It fits for setting and time reference.

Thanks! That is enough to explain it for me.