Clue: 17 stuck halfway through Paul, Tramp, Vlad, even Rufus? Yes, initially (5)
Answer: ULTRA
Explanation: Definition: 17
The "middle" of paUL TRAmp, and the first letters of Vlad Even Rufus Yes give VERY, which could mean "ultra, e.g. "this is an ultra-clever clue". This and 17d cross-reference each other, so there's no actual definition except in the answers