This dream seems pleasant enough from the outside to be worth investigating, so the TARDIS follows the tug of the telepathic current until she manifests in a cozy little alcove off a grand ballroom (no match for her own on a good day, though). The somewhat severe looking blue dress and cap she appears in isn't what she'd had in mind, but besides the mild vexation of having her psychic avatar's appearance manipulated, it doesn't seem immediately offensive, so she lets it slide. This is apparently supposed to be a costume party, anyway. Perhaps Ianto could throw one in celebration of those human Halloween festivities and she could show the guests a real grand ballroom.

The TARDIS goes on her way amongst the party-goers, letting their enjoyment trickle against her awareness, critically regarding the ostentatious trappings of the location, and looking for snacks or familiar minds, in that order.