No one in the department( but Peter and I) knows that the director is going to resign.这里no one是主语,knows做它的谓语动词,that引导宾语从句,but Peter and I 可以理解为一个插入语:除了皮特和我
由 along with, as well as, as much as, accompanied by, except, but, in addition to, including, more than, rather than, together with, instead of, like 等引导的介词状语放在主语后,对主语的数不产生影响。
如:No one but you knows the truth.
The teacher as well as the students likes this novel.