Lost in Camelot (Merlin Fanfic, Arthur/merlin; Bradley/colin)

When Merlin killed Nimueh, the powerful magic produced huge energy, opening a passage between two parallel worlds. One day the cracks moved and Arthur, Merlin and Bradley, Colin passed through each other. The opened passage threatened several nearby parallel worlds, so Doctor and Jack traveled from another parallel world to repair the cracks. As a result, they encountered crack activity, and the Tardis fell half-destroyed, temporarily trapped in the parallel world...