What's the pun in this "Julius Caesar" reference?

In a Blacklist episode, the following conversation takes place, the first and last speaker is the sophisticated Raymond Reddington:

-'Ambition's debt must be paid'.

-Julius Caesar?

-One of my favorites. The play, not so much the man. The man was a bit full of himself. He did have a brilliant military mind, but he couldn't smell a plot to save his life. Intentional pun.

I cannot for the life of me understand the joke. My only hypotheses circle around the words plot - also a place for a grave - and the mention of smell in the following soliloquy from the Shakespeare play, but I have found nothing satisfying:

Antony:

O, pardon me, thou bleeding piece of earth,
That I am meek and gentle with these butchers!
Thou art the ruins of the noblest man
That ever lived in the tide of times.
Woe to the hand that shed this costly blood!
Over thy wounds now do I prophesy,--
Which, like dumb mouths, do ope their ruby lips,
To beg the voice and utterance of my tongue--
A curse shall light upon the limbs of men;
Domestic fury and fierce civil strife
Shall cumber all the parts of Italy;
Blood and destruction shall be so in use
And dreadful objects so familiar
That mothers shall but smile when they behold
Their infants quarter'd with the hands of war;
All pity choked with custom of fell deeds:
And Caesar's spirit, ranging for revenge,
With Ate by his side come hot from hell,
Shall in these confines with a monarch's voice
Cry 'Havoc,' and let slip the dogs of war;
That this foul deed shall smell above the earth
With carrion men, groaning for burial.

Solution 1:

The pun is on 'couldn't (do something) to save his life'.

Usually 'to save his own life' is used metaphorically, meaning that he couldn't do X very well. Except here the X, 'discovering a plot', is what he couldn't do and he literally could not save his own life because of it, the plot was to kill Caesar.

As everyone else said, it's not a particularly strong pun, because it is based on the weak difference between metaphorical and literal meanings, rather than very distinct meanings or close sounding words, but it is technically a pun.

Solution 2:

" He couldn't run to save his life;"

"He couldn't swim to save his life;"

morphed into such phrases as

"He couldn't play bridge to save his life." "...fry eggs..." "...tie a reef knot..."

Here R R finds himself using the phrase literally. I think that is the play on words that catches him by surprise, an informal phrase in a real context.