to take a leap in the dark.
http://tinyurl.com/pyjcl2e
take /run a risk: to expose oneself to the chance of injury or loss; put oneself in danger; hazard; venture.
http://tinyurl.com/o8f9ubt
Beard The Lion in His Den
If you visit someone important in the place where they work, in order to challenge him/her or obtain something, you beard the lion in his den.
معنی فارسی:دل به دریا زدن، با شیر دست و پنجه نرم کردن, به کنار شیر رفتن
Example:
- If he continues to refuse my calls, I’ll have to beard him in his den.
http://tinyurl.com/qbmjo2m
http://tinyurl.com/nnvfwfj