过去分词不能作主语，这是原则。这是倒装句，主语为后面的名词。你肯定在疑惑后面是and并列的二个名词，谓语动词怎么能用is？你忽略了means作途径、手段解的时候是单复数同形的。在此是单数名词，二个单数名词共用一个不定冠词a, 说明这是同一个事物的不同用途而已。例如下句：

His wife and secretary was with him. 注意wife和secretary共用一个限定词his，表示这是一人身兼二职，他老婆和秘书是同一个人，当然谓语动词要用单数。

HIs wife and his secretary were with him. 重复限定词，表示这是二个人，所以谓语动词用复数。

把第一个例句倒装一下：

With him was his wife and secretary. 这就和你的句子结构一样了。