Predicting a "dark horse" stock—one that could surprise the market with a significant upside or unexpected performance—can be tricky, as it depends on various factors like earnings reports, sector news, or unexpected events. However, I can point to a few general strategies or sectors that might have potential for surprises:

1. **Tech Stocks**: With the ongoing AI revolution, companies heavily involved in AI, cloud computing, or semiconductors might see sudden spikes. Look for smaller companies or those that are less talked about compared to the giants like Nvidia or Alphabet. **SMIC** (Semiconductor Manufacturing International Corporation) or **Micron** might be worth keeping an eye on for potential upside.

2. **Energy Stocks**: With fluctuating oil prices, energy companies that are more sensitive to price swings might have volatile but interesting movements. Companies like **Occidental Petroleum** or **Pioneer Natural Resources** could have upside if oil prices rise.

3. **Consumer Discretionary**: Stocks in this sector can be more volatile, but companies with strong brand loyalty or those that benefit from short-term trends could surprise. **Lululemon** or **Home Depot** often deliver unexpected results if the consumer spending trend is stronger than expected.

4. **Small-Cap Growth**: Smaller companies often have more room to grow or be revalued unexpectedly, especially those with recent earnings beats or product innovations. These could be under-the-radar stocks that get a pop on news.