The Sontaran Experiment

As you promised Vira you'd look into the malfunctioning transmat, you send Harry off to fetch Sarah whilst you get to work on one of the silver globes.
A few minutes later, Harry reappears with a slightly moody Sarah in tow. You pretend to be ensconsed in the globe and pull out your sonic screwdriver.
"Shall we explore a bit?" asks Sarah.
"If you want," you reply. "Trafalgar Square's that way," you continue, pointing vaguely in the opposite direction from where Sarah and Harry have set off.
Sarah and Harry disappear over the brow of the hill and you set to work on the sphere.
After a while, you hear rustling in the undergrowth. You think you can see a man in the distance watching you, but pretend not to have seen him.
Do you carry on working on the sphere, or try to find out who he is.