Factual error: The number plate on the black cab is GW22 ARY. This won't happen until the year 2022. (00:28:20)
Character mistake: When they've worked out that the kidnappers were changing flood maps, Harlan says he "doesn't get why anyone would mess with flood maps in the first place." Looking at the maps it's blatantly obvious that the reworked flood zone excludes a chunk of land, and given property prices in New York it doesn't take a genius to figure it's at least connected to real estate, insurance, etc. Harlan is demonstrably a genius, and could certainly have figured that out for himself.
Continuity mistake: Just before Sherlock and Detective Bell enter the dead professor's office, both are putting on gloves. Sherlock puts on the left first and has partially put on the right. As they enter the office, Sherlock still hasn't put the right glove on at all - he's just starting to do so. (00:05:30)
Continuity mistake: Watson came to Mycroft's place, spent the night and was awoken by Sherlock (this episode) the next day. Somehow she had a nightie and a brand new outfit. (00:00:05)
Answer: I'm the same person who asked this question. I discovered it was Molly Price whom I recognized from Third Watch.
Cathrine R
It should be noted Donna was Jim Fowkes‘ secretary. Donna killed Peter.
Bishop73