Theory:Doctor Who television discontinuity and plot holes/Fury from the Deep


 * Why does the Doctor rely on Victoria's hairpin to open doors rather than using the Sonic screwdriver?
 * The sonic screwdriver is new to the Doctor, at least in terms of carrying it around with him. He clearly had not yet thought to use it in its later regular role as a lockpick.
 * Victoria is deeply upset and traumatised during this story, and the Doctor knows from experience that giving her something to be proactive with and achieve works wonders with the poor girl; hence, although the sonic screwdriver may be able to be used as a lockpick, even if he's actually thought of using it that way at this point, he'd probably decide it was best to let Victoria handle the locks.
 * It's a sonic screwdriver, not a sonic lockpick. Unlike modern versions of the device, this sonic screwdriver drives screws using sound waves. It doesn't really seem to become a multipurpose tool until the 3rd Doctor's time.
 * In fact it becomes more of a multi purpose tool first in the 2nd Doctor story the Dominators where the Doctor uses it to burn thru the wall in the fall-out shelter on the Island of Death on Dulkis.
 * It didn't become the magic wand we all know nowadays until Rose