How much blame can be given to Mr. Denny and the Forsters? The Forsters were (obviously) not particularly vigilant about Lydia’s activities or acquaintance although I am sure they did not expect her to act so foolishly. After the elopement Col Forster admitted he had “often suspected some partiality, especially on Lydia's side, but nothing to give him any alarm” and he “did not speak so well of Wickham as he formerly did. He believed him to be imprudent and extravagant” According to Lydia’s letters Mrs. Forster was continually taking her to the camp and knew which gentleman was her favorite:

When Lydia went away, she promised to write very often and very minutely to her mother and Kitty; but her letters were always long expected, and always very short. Those to her mother contained little else than that they were just returned from the library, where such and such officers had attended them… was obliged to leave off in a violent hurry, as Mrs. Forster called her, and they were going to the camp… (42)

"You will laugh when you know where I am gone, and I cannot help laughing myself at your surprise to-morrow morning, as soon as I am missed. I am going to Gretna Green, and if you cannot guess with who, I shall think you a simpleton, for there is but one man in the world I love, and he is an angel. I should never be happy without him, so think it no harm to be off." (47)

I think the Forsters were ill prepared to chaperone Lydia and although they were negligent at least the Forsters do not appear to be duplicitous or worse as does Mr. Denny. He obviously knew of the “elopement” and that it was a lie on Wickham’s part:

Though Lydia's short letter to Mrs. F. gave them to understand that they were going to Gretna Green, something was dropped by Denny expressing his belief that W. never intended to go there, or to marry Lydia at all, which was repeated to Colonel F… (46)

An elopement is a bad enough adventure but Denny shows himself to be nearly as wicked as Wickham in letting the “elopement” happen although he knew it was a sham and Lydia would be ruined and probably abandoned. It shows that he had no care for Lydia although he has supposedly been her friend for quite a while—he is not much of an officer or a gentleman. He allows Wickham to run out on the debt he owes to their fellow officers and he could have prevented a scandal in his commanding officer’s house. Is Denny really so loyal to Wickham or is he just trying to save his own hide; his refusing to confirm that he had known beforehand Wickham had no intention of marrying Lydia could attest to either reason for his silence. Either way he is a coward not to admit the truth:

"And was Denny convinced that Wickham would not marry? Did he know of their intending to go off? Had Colonel Forster seen Denny himself?"

"Yes; but when questioned by him Denny denied knowing anything of their plan, and would not give his real opinion about it. He did not repeat his persuasion of their not marrying -- and from that, I am inclined to hope, he might have been misunderstood before." (47)