This time, the shadowy voice belongs to Arturo Taccone. Yikes.
He tells her that he will "take a great many pains, if you will" (5.13) to get his paintings back. Our Spidey Sense tells us that he doesn't mean his own pains. He means something more like a breaking Kat's knees in the middle of the night. Or worse.
Kat tries to tell him that her father didn't steal the paintings, but he gives her a deadline to return the paintings anyway: two weeks.
Back at Hale's mansion, Kat fills Hale in on what's going on. She tells him that they are going to get Taccone his paintings back... by stealing them, obviously.