Much like secretaries, librarians are also hot -- the younger ones, anyway. Zoe is one such librarian with one added detail: she's from the future. She works aboard the space station W3, also known as the Wheel. She aids the Doctor in stopping a Cyberman invasion and quickly joins him aboard the TARDIS for more adventure. Aside from being hot, Zoe is also a genius, solving complex mathematics with the speed and certainty of a high-tech computer. Now, her age is a bit of a mystery, but the actress playing her was at least 20 at the time, so calling her hot totally doesn't feel creepy.
