The Thumb Drive is the key to fix Holmes and bring him back to normal. You will use this when you meet him (Holmes is actually a computer that talks). Once you hear him sing a song about Marry have a little Lamb, Dr. Harold will appear to give you the island medallion. This will be the last item that you will get in the island.
How to Get the Thumb Drive
Finish all 4 Game Shows namely Super Terrific, Scaredy Pants, Brainiacs, Kerplunk and Spin for Riches and you need to win to these games. Once you completed these game show, go back to the Main Street using your Jet, when you arrive Holmes will call the attention of all robots to apprehend you. You will hear a whistle came from the hole near a tree. Go down to the left and enter the hole. You’ll get into Holmes’ Inner Sanctum and you will see Dr. Harold again. This is the place where he commands all robots and Dr. Harold will give you the Thumb Drive that will fix everything.