Complex sentence: We are first introduced to Mary in The Empty Hearse when Watson is attempting to propose, however Sherlock interupts surprises John to let him know that he (Sherlock) is'not dead'.
Split into simpler sentences: We are first introduced to Mary in The Empty Hearse when Watson is attempting to propose. However, Sherlock interupts surprises John to let him know that he (Sherlock) is'not dead'.