暗察明访

Explanation: Review: a closer look, sifted; visit: search. Means the investigation to understand the situation in various ways 　　Usage: As the predicate attribute; for praise 　　Source: "Kim Shi Shizong Jizhong": "These types dark Chaming visit, all the political noise." 　　Examples: After ~, we finally found the crux of the problem Thesaurus:  Thorough investigation, Ming Zha make secret inquiries