Thales is one of the main characters in the poem. He's planning to leave London to try to find a more peaceful, less sinful life in the country. At the outset, the speaker supports his choice even though he regrets knowing that his friend is going to leave.
At times, Thales makes references to historical figures like King Edward, whom he sees as noble. He also calls King Henry victorious. He speaks about how, under King Alfred, one jail was enough for half of all the criminals. He says Alfred was fair. These references are set in contrast to the way he sees the current government, which makes criminals out of far too many.
Thales rants for some time about life in London. It's clear that it's a dangerous place where men are victimized if they don't have the right power and connections. The city is rife with sin; there are murders, rapes, and other serious crimes occurring, and no one is able to stop them. The noble character of London has changed for the worse.
Even at the end of the poem, Thales still isn't done expressing his discontent. He tells his friend that he could continue to air his grievances. However, his boat is approaching, and his time in London is done. He encourages his friend to join him one day when his "youth, and health, and fortune" are gone.
The speaker has gone to the Thames to wait with his friend for the boat that will ferry him away from London. He recognizes the evils of their society in London but is clearly not planning to leave with his friend. Something about that lifestyle drags him back again, even though he believes that it's a healthier and smarter choice to leave. He even discusses the sins of London before his friend begins to speak, saying that those who don't give in to hunger are worn down by age. He refers to malice, rape, and accident.