How to save the world in an Alternate Timeline and make it back for... supper, at least

The thing about alternate universe, or the thing about multiple universes, wasn't so much of the differences between them, as fun as they may be. It was the similarities, the multiples, if you will, that opened up opportunities. Wasn't it knowledge of their own world that saved their lives in the altered one, after all?That was not the point. The point was, despite everything that had been changed, events that transpired independently from another universe's interference would go the same way, (similarities unaltered, after all,) which is why on a normal Thursday work afternoon, Irina comes across what seems to be the most curious little device.Or: There are two sets of time-travel headache-inducing thingadings, and too many people after them.