In Saint Erasmus's Catholic Church, there's a parish register containing a firsthand account of the sinking of the San Telmo. Chris and Carrie must find the register to find the ship and honor their aunt. All they have to do is break into the church--while lying to their friend Maddison about basically everything. Not to mention the church is supposed to be very haunted.
Secrets of the Old Church is book #2 from Treasure Hunters, an EPIC Press series, a division of ABDO.