The Diamond Sword of Tor
by Robert A.V. Jacobs
But now, after five centuries, the sword hidden behind a disguise of steel, has found its way into the hands of Erun Oncant, Sovereign King of Cardoney.
A child at play caused the portal to allow a single team of humans through, and they need to recover the key to return home. When they don’t find it in the castle, they kidnap the Queen, to coerce Erun into returning it.