Plan B.
A fallback plan in case the original goes wrong. Usually instituted after:-

Plan B is usually actioned when not expected to be needed and as a result, often made up 'on the fly'. In the age old tradition of things, it would not be a proper Plan B if it had been planned in advance.

See also:
Lose with a little panache

The name of a "morning after pill" (levonorgestrel), which is available on prescription. --Oolong