I'd start here (there's an email contact at the top of the page):
https://www.curtisbrown.co.uk/client/david-farr------------------------------
Michael McDonough
TRW Director of Amateur Licensing
New York
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Original Message:
Sent: 07-20-2017 07:38
From: Elisabeth Ledwell
Subject: The Heart of Robin Hood
Does anyone know who holds the rights to this play? I saw it at American Repertory Theatre in Boston five years ago and bought the escript, but it doesn't list the rights. I have not been able to find it in any of the standard places.
Sent from my iPad