Black Cat is a master of theft. The girl loves riddles and puzzles. She left some toys hidden around the city - it's up to Peter to find them and reveal her true whereabouts.
Black Cat Riddles are always based on one principle - reach the telescope atop a building and use it to locate the toy. It's not really difficult, and the game provides some tips, still. The first is a characteristic glow. The toys twinkle periodically. The other hint is graffiti - a painting is always near the toy cat. It's really hard to miss.
Completing all 12 Black Cat's puzzles unlocks the "Cat's Cradle" side quest. You will reach the girl's hideout and get a special suit - the Dark Suit.