By David Russell, reporter at OptionMonsterNEW YORK -- Fast-money traders went shopping in Gap ( GPS) on Monday morning. OptionMonster's tracking programs detected unusual activity in the Weekly 30.50 calls expiring this Friday, with early buying for 69 cents and 70 cents. Some 1,300 contracts had traded in the first few minutes of the session, followed by another 1,300 throughout the rest of the day. Gap shares were marginally higher at the time and then started to ramp higher, ending the day up 2% to $31.04. But that was nothing compared with the 30.50 calls, which shot up 50% to $1.05. That made for some fast money from a minuscule move in the stock price. Calls lock in the price where investors can buy shares, providing tremendous leverage in the event of a rally. But if it doesn't go in the right direction, they can be rendered worthless just as quick. The apparel retailer hit a multi-year peak near $38 in October before rolling over, and it's now trying to find support around the key $30 breakout level from the summer. The company is scheduled to report December same-store sales Thursday morning, which could provide a catalyst. More than 21,000 option contracts changed hands in the name on Monday, about four times its daily average for the last month. Russell has no positions in GPS.