Kieran and the Weird Window

Kieran, a teen-age boy, out of curiosity, goes into his father's basement workshop and discovers a window that's not a window. It turns out to be some sort of wormhole. He brazenly steps through the weird window into another workshop in another universe. He encounters a boy from that universe and they both discover that their fathers know each other and have been working together for years. One serious problem is that the weird window is unstable and comes and goes with no apparent pattern. This causes all sorts of problems, among which is that it's easy to be stranded, which is indeed what happens.