Buffett's $4.
1. Berkshire Hathaway increased holdings by $4.8 billion in Q1 and Q2. 2. Mystery stock is not in banks, insurers, or consumer products, narrowing options. 3. Speculations suggest potential investments in logistics firms like UPS and FedEx. 4. The secret could surprise; previous investments included unexpected companies. 5. Third-quarter filings to reveal mystery stock expected by mid-November.