1. There were many political heavyweights for whom Mary was a legitimate, attractive alternative to Elizabeth.

【解析】for whom Mary was a legitimate, attractive alternative to Elizabeth是限定性定语从句修饰后表示人且在定语从句中做介词for的宾语的先行词heavyweights。

2. They were not just a bunch of wild-eyed Catholic dreamers, but men close to the heart of Elizabeth's government.

【解析】这句话用not...but...来连接并列的表语成分，一个是：a bunch of wild-eyed Catholic dreamers（一群狂热的天主教追随者），另外一个是：men close to the heart of Elizabeth's government（伊丽莎白政权的核心人物）。

在第二表语中，close to the heart of Elizabeth's government是带有介词的形容词短语作后置定语，修饰名词men。

3. Their most ambitious plan was to annul the Bothwell marriage and marry the Queen of Scots to the premier duke of the realm, Thomas Howard, Duke of Norfolk.

【解析】这个句子是用并列连词and连接了2个并列分句，一个是：Their most ambitious plan was to annul the Bothwell marriage（他们的野心勃勃的打算废除和博思韦尔的婚约），另一个是：marry the Queen of Scots to the premier duke of the realm, Thomas Howard, Duke of Norfolk.（让苏格兰女王嫁给王国第一公爵诺福克公爵，名字叫做托马斯·霍华德）。

在第一个分句中，谓语是be+动词不定时表示将来发生的事情。

在第二个分句中，Thomas Howard是做duke 的同位语，补充说明duke的名字。Duke of Norfolk是做Thomas Howard的同位语。

4. Although Norfolk may have been a Catholic at heart, he was, like so many of this time, outwardly at least, a conforming Protestant.

【解析】这是含有让步状语从句的复合句。主句是：he was, like so many of this time, outwardly at least, a conforming Protestant，让步状语从句是：Although Norfolk may have been a Catholic at heart。

在主句中like so many of this time（就像这个时代这么多人一样）是作方式状语，outwardly at least（外表上看来至少）是做程度状语，a conforming protestant（顺服的天主教徒）是做表语。

5. There was, though, a different kind of fury waiting to happen.

【解析】waiting to happen是现在分词作主语fury的补足语。