Query Critique #2

Thanks for submitting , Deniz! The original is in blue; comments are in black; suggested text is red. Again, please feel free to adapt, disregard, or change any of my suggestions.  

Dear [agent],

I am seeking representation for my 90,000 word young adult historical fantasy THE FACE OF A LION, centred around the time of the Roman invasion of Britain.
While this is an acceptable way to start a query letter, I recommend opening with something to hook the reader.  The agent already knows that this is a query, particularly if you put "Query" in the subject line of your email.

THE FACE OF A LION features 13-year-old Austin and a magical cat named Kedi.
This is a passive way to introduce the characters.  I suggest incorporating this information into the action.

His parents rent a villa in Turkey for the entire summer and Austin gets set for the most boring vacation of his life, away from all his friends in England. But that's before he rescues a talking cat, witnesses a bloody ritual that causes two people to disappear, and suddenly finds himself whisked back in time.
Now we're getting to the meat of the query. This premise is fascinating, but I think it should come out sooner to hook the agent's interest. I suggest that you avoid words like "boring" in your query, since they don't sell your work. I'll also mention that, since kids tend to "read up," age-wise, you might consider either aging your character a few years or marketing this as a Middle Grade book.
When thirteen-year-old Austin's parents drag him along to a villa in Turkey they've rented for the summer, he hunkers down and counts the days until he can get back home to his friends in England. But that's before he rescues a talking cat, witnesses a bloody ritual that causes two people to disappear, and finds himself whisked back in time.

In Ephesus, nearly 2000 years in the past, he makes a new friend, falls in love – and finds an enemy. Evil forces are at work, doing their best to prevent Claudius the Emperor's invasion of Britain, and Austin has to act fast to figure out how to influence the Emperor and ensure that the invasion does take place. It's either that, or time and civilization as he knows it will never be the same.
This is a good taste of the conflict, but the wording could be tighter. Something about the term "evil forces" seems too vague, but I'm not sure of the alternatives without reading the MS. If you have a unique villain, though, here's a great time to mention him/her. I'm also a little taken aback by the idea of a 13-year-old falling in love--is it more of a crush? That seems more age-appropriate (yes, I know Romeo and Juliet were 14 and 13, but we're talking about a 21st century kid here--and trying to sell this MS in the current YA market). Beware of using the passive voice too much, as well.
Nearly two thousand years in the past, he makes a new friend--and a new enemy. A powerful evil wants to prevent Claudius the Emperor's invasion of Britain. Austin has to act fast to ensure that the invasion does take place--or time and civilization as he knows it will never be the same.

THE FACE OF A LION focuses on the themes of friendship and loyalty, as well as exploring the ideas of time travel and the day-to-day decisions we make, for good or bad, that can have far-reaching consequences.
I like this, but the wording could be tighter. I've also brought down the info from your opening. I've also re-worded to remove the first-person-plural "we," since queries should be in the third person. 
THE FACE OF A LION focuses explores the ideas of friendship and loyalty, time travel, and the far-reaching consequences of good or bad decisions. This young adult historical fantasy is complete at 90,000 words.

Can Austin come up with a plan that will save his world?
I've NEVER seen an agent who likes rhetorical questions, but I've heard from several who loathe them. I suggest avoiding them and cutting this line, since this conflict has already been presented.

Please let me know if you would be interested in seeing the manuscript of THE FACE OF A LION.
This is a nice closing line, but it's not necessary. Agents know to contact you if they want to see more. This would also be a good place to include your bio.  I'm guessing from your name--and the name of the talking cat--that you have some familiarity with Turkey (Ben de Turkiye'de yasiyordum). I'd mention this connection, as well as a background in history, if you have one. Try to keep it to 1-2 sentences.

Sincerely,

Deniz Bevan