What does the cryptic crossword clue "The key part of a Houdini contract? (6,6)" mean?

The definition is "The key part of a Houdini contract?". The wordplay uses a cryptic definition. Cryptic definition The answer is ESCAPECLAUSE.

The key part of a Houdini contract? (6,6)

Guardian Cryptic #27311 | 14 Across | 2017-09-25 flower