Possible Clues:

• Missing parcel inquiry
• You can see like a shot it's fast at last
• One looking for a radioactive isotope
• Lost package inquiry
• Bullet whose track can be seen - element tracking radiation
• Such bullets go so fast at last you can see them
• Lost-parcel locator
• On the track, time runner
• U.P.S. inquiry
• You may see how fast it's shot after tea