Although we don't believe in timing the market or panicking over market movements, we do like to keep an eye on big changes -- just in case they're material to our investing thesis.

What: Shares of property and liability insurer Alleghany (NYSE: Y) plunged as much as 10.1% on very heavy morning trading.

So what: Thanks to a sweetened offer filed Friday night, Alleghany is winning a bidding war over reinsurer and former AIG (NYSE: AIG) subsidiary Transatlantic (NYSE: TRH). The market reaction indicates that investors would rather see bidding rivals Validus (NYSE: VR), Allied World (NYSE: AWH), or even Berkshire Hathaway (NYSE: BRK-B) walking away with the prize, given the rapidly rising buyout prices.

Now what: Transatlantic's largest shareholder, Davis Selected Advisors, has opposed earlier bids, but likes this one. That's a sure sign that Alleghany isn't getting much of a deep-value deal here, and with this many serious suitors in line you really have to accept a big price tag. Is Alleghany walking away with the belle of the ball, or will another cavalier raise the price once again? The only way to know for sure is by keeping a close eye on the whole gang: