Complex sentence: Holmes and Watson can rarely have been faced with such an uncooperative and unusual client, and they have just forty minutes to find out what problem has brought him to 221B Baker Street before the heavy boots of the official police force start clumping up the stairs.
Split into simpler sentences: Holmes and Watson can rarely have been faced with such an uncooperative and unusual client. They have just forty minutes to find out what problem has brought him to 221B Baker Street before the heavy boots of the official police force start clumping up the stairs.