Actually, second stop fourteenth-century Constantinople. First stop, your local pet shop, where you'd buy a couple of dozen cats. Then fourteenth-century Constantinople, where you release the moggies in the cargo holds of the rat-infested grain ships on their way to spread the Black Death throughout Europe. Then fast-forward to seventeenth-century London, with your fire extinguisher under your arm --
Not so fast. By stopping the Black Death in its tracks, you've changed history. True, you've saved a third of the population of Europe from a horrible, lingering death. Which means, no fourteenth-century labour shortage, which means the feudal system doesn't collapse, which means you're too busy ploughing the Earl of Middlesex's estate by lantern-light with a team of oxen to go larking about time-travelling.
This is why a) we have time cops and b) we generally refrain from time traveling.
