Clue: Nothing to be found between 13 down and 28 (4)
Answer: LOVE
Explanation: Definition: Nothing
~~If you put O (zero, nothing) between 13d and 27a then we see ordina**L O VE**nue; it's not really an &lit (aka clue as definition), but that's the general idea~~ *Ignore that rubbish: it's hidden in celLO + VEnue – thanks wooden_tree